mips: octeon: cpu.c: Add arch_misc_init() for pci-console & pci-bootcmd

This patch adds the necessary platform infrastructure code, so that the
MIPS Octeon drivers "serial_octeon_pcie_console" & "serial_bootcmd" can
be used. This is e.g. the bootmem initialization in a compatible way to
the Marvell 2013 U-Boot, so that the exisiting PC remote tools like
"oct-remote-console" & "oct-remote-load" can be used. This is be done in
the newly introduced arch_misc_init(), which calls the necessary init
functions when enabled.

These patches are in preparation for the MIPS Octeon NIC23 board
support, which is a desktop PCIe target board enabling these features.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Aaron Williams <awilliams@marvell.com>
Cc: Chandrakala Chavva <cchavva@marvell.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>