mtd: nand: NFC drivers for RK3308, RK2928 and others

This driver supports Rockchip NFC (NAND Flash Controller) found on
RK3308, RK2928, RKPX30, RV1108 and other SOCs. The driver has been
tested using 8-bit NAND interface on the ARM based RK3308 platform.

Support Rockchip SoCs and NFC versions:
- PX30 and RK3326(NFCv900).
	ECC: 16/40/60/70 bits/1KB.
	CLOCK: ahb and nfc.
- RK3308 and RV1108(NFCv800).
	ECC: 16 bits/1KB.
	CLOCK: ahb and nfc.
- RK3036 and RK3128(NFCv622).
	ECC: 16/24/40/60 bits/1KB.
	CLOCK: ahb and nfc.
- RK3066, RK3188 and RK2928(NFCv600).
	ECC: 16/24/40/60 bits/1KB.
	CLOCK: ahb.

Supported features:
- Read full page data by DMA.
- Support HW ECC(one step is 1KB).
- Support 2 - 32K page size.
- Support 8 CS(depend on SoCs)

Limitations:
- No support for the ecc step size is 512.
- Untested on some SoCs.
- No support for subpages.
- No support for the builtin randomizer.
- The original bad block mask is not supported. It is recommended to
  use  the BBT(bad block table).

Signed-off-by: Yifeng Zhao <yifeng.zhao@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>