ppc/85xx: add cpu init config file for boot from NAND

When boot from NAND, the NAND flash must be connected to br/or0.
Also init RAM(L2 SRAM or DDR SDRAM) for load the second image to
it.

Signed-off-by: Mingkai Hu <Mingkai.hu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>