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ARC fixes for 2022.07

A minor build fix for HSDK, kudos to Corentin Labbe.

Here we improve clock support for recently introduced HSDK-4xD
board as well as finally enable external reset for the USB controller,
which is needed to recover USB functionality after "usb reset".

Here we introduce new development platfrom for ARC: HSDK 4xD.
That's pretty much the same base-board as in HSDK but with
very recent quad-core ARC HS47D in the ASIC.

Thus we try to re-use existing code as much as possible while
inevitably add some pieces needed for the new ASIC.

Also we drop selection of bounce buffers on AXS10x
as there's no use of them any longer.

This is pretty minor set of changes mostly touching HSDK board:

 * Enable on-chip reset controller on HSDK
 * Add possibility to turn-on & off L2$ on more
   recent ARC HS processors.
 * AXI tunnel clock calculation on HSDK

This last minute pull-request is intended to fix some drivers
when used on ARC boards. The problem was introduced by
https://gitlab.denx.de/u-boot/u-boot/-/commit/07906b3dad157bd58411664bcc6a2a7976d5e0a9

What happened while doing one pretty simple improvement to make
U-Boot port more flexible and portable (by switching accessors from
assembly-written to plain C version) we implicitly added 2 problems:

 1. Downgraded accessors from being volatile which signalled to
    the compiler that it's now possible to do all kinds of optimizations
    which may easily include merge of subsequent byte reads/writes into
    word operations. Which is OK for accessing mormal memory but
    breaks operation of peripherals if we access its memory-mapped regs
    in such a "creative" manner.
 2. As a part of assembly-written implementation we had compiler barriers
    in form of the following construction 'asm volatile("" : : : "memory")',
    and we dropped it in C implemntation. This in its turn enabled compiler
    to mess with instruction ordering. Guess what it gives us in the end :)

So with all that we had in some corner-cases veeery funny instruction flows
generated. And in particular it broke DW SPI functionality when we were
writing large amount of data. Funny enough our tests which were writing
small amount of data still worked and only by the chance we caught that
breakage and unrolled that quite interesting loop of unexpected
problems.

The road to hell is paved with good intentions. Amen :)

As usual a bit late a couple of tiny fixes and improvements for ARC.

1. Switch from ARC UART to a convenient DW UART on ARC
   simulation platforms. This became avaialble when nSIM got support
   of that much more standard UART (starting from nSIM v2019.06).
   FWIW also available now in Free nSIM [1].

   This among other things allows us finally to use the same one binary
   on all our simulators & FPGA-based emulators.

2. Disable networking support on simulated platforms as there's no
   network interface in them.

3. Add Virtio net & block devices for the configuration supported
   by QEMU so that we may leverage those virtual peripherals and
   in fact it's possible to load uImage from TFTP server and bootm it.

4. Minor fixes for HSDK clocks.

5. Rework of how we chose and use compiler options for ARC-based boards.
   In real world ARC-based designs are customized more or less but very
   rarely match any of our "templates" thus it makes not much sense to
   pretend we have some fixed configs, instead we now will fully reply
   on a SoC or even board on getting precise set of compiler options
   preferably even extracted from real HW via "tcfgen" utility.

6. Well and finally yet another simplification - switch to generic
   written in C accessors which are much more universal and just work
   for any target supported by the complier as compared to GAS
   implementation which is much more target-dependent.

   This one was heavily "inspired" by similar implementation for RISCV
   and ARM.

[1] https://www.synopsys.com/cgi-bin/dwarcnsim/req1.cgi

ARC fixes for v2020.01-rc2

The main change is move to DM_MMC of yet 2 another ARC boards:
AXS101 & IoTDK.

Among that we improve handling of stock-formatted SD-cards of high volume
on EM SDP as well as introduction of reset driver for HSDK which is required
for prepser reinitialization of some peripherals like USB etc.

These are some very late changes mostly required to get 64-bit
division working on ARC boards.

For that we had to import missing parts of libgcc and add compiler
flags to EMSDP which otherwise used very simple profile for compliation.

And while at it another fix for EM SDP initialization is inluded as well.

In this small series we migrate ARC boards to DM_MMC
so we're hopefully are good now and our boards will be kept
in U-Boot for some more time :)

This is last minute change which fixes problems in runtime on
AXS10x board caused by some changes in NAND framework and
tiny documentation improvement.

Anyways NAND flash storage was never really used on the board for various
reasons and now we decided to drop it for good.

Note this change only touches 1 ARC board so that should be safe for others.
As usual - build tested in TravisCI, see
https://travis-ci.org/abrodkin/u-boot/builds/512041342

A couple of trivial fixes and improvements for ARC

Most notable are:
 * Move of ENV_SIZE/ENV_OFFSET to Kconfig
 * Fix with private structure allocation for arc_uart
 * Definition of CONFIG_SYS_CACHELINE_SIZE useful for building drivers

We introduce much better automatic identification of ARC cores.

 1. Try to match found HW features to known ARC core templates
 2. Print CPU frequency for all ARC boards
 3. Add more board-specific info

Just 2 non-functinal changes:

 1. Rename of EMDK to EMSDP so it matches real marketing name
 2. Add essential README for IoTDK

More fixes and improvements for ARC here:

Fixes (this time included for real):
 * Take care of global uninitialized variables
   They used to be put right after .bss section and were never
   zeroed as they should be. Now merged with normal .bss

Improvements:
 * Print more verbose CPU info for boards built on real silicon
 * Add support for SD-card detection on all ARC boards
 * Quite a few fixes for IoT DK
   - Support reset by command
   - Print of CPU freq on boot
   - Link for eFlash etc

More fixes and improvements for ARC here:

Fixes:
 * Take care of global uninitialized variables
   They used to be put right after .bss section and were never
   zeroed as they should be. Now merged with normal .bss

Improvements:
 * Print more verbose CPU info for boards built on real silicon
 * Add support for SD-card detection on all ARC boards
 * Quite a few fixes for IoT DK
   - Support reset by command
   - Print of CPU freq on boot
   - Link for eFlash etc

Here we do a couple of impovements for all ARC boards
as well as introduce yet another developemnt board.

1. Now for ARC boards we print CPU and board info
   which is useful for users and helps with
   analysis of logs "post-mortem".

2. Synopsys IoT development kit support is added
   This one might bw a bit too late as we're past RC1
   but:
    1) This doesn't affect any other arches etc
       as we change purely ARC code.
    2) I've got a chance to talk about U-Boot on
       IoT platforms during ELCE (my proposal was on
       a wait list and only this week I've got
       an update and invitation to talk) so it would
       be good to have this board as a primer in upstream
       code-base by the time of ELCE 2018.
    3) For complete support of IoT devkit I'm yet to
       significantly rework regmap subsystem in U-Boot
       but that's a different topic and hopefully it will
       be done sometime soon... though not this release
       cycle for sure.

Minor changes for ARC

1. Fix CPU clock value in HSDK's .dts so time is counted properly.
2. Enable bootelf command on EMDK

That's a set of prety minor changes and fixes for ARC.

Among them:
 * Improvement in CREG GPIO driver used on ARC dev boards
   that allow us to re-use the driver for SPI's chip select

 * Enable SPI-flsh on AXS10x boards which allows to update
   U-Boot binary that gets loaded by boot-ROM

 * Fix accommodating always utilized unaligned access by
   GCC for ARC starting from 8.1.0

Here we only add readme file for EMDK board
support of which was added in this release cycle.

Here we just add a tool for HSDK flashable images preparation
together with extensive documentation for HSDK board.

This will help real-life users to update U-Boot on the board.