NAND: Add NAND support for MPC8536DS board

This patch defines 1M TLB&LAW size for NAND on MPC8536DS, assigns 0xffa00000
for CONFIG_SYS_NAND_BASE and adds other NAND supports in config file.
It also moves environment(CONFIG_ENV_ADDR) outside of u-boot image.

Singed-off-by: Jason Jin <Jason.Jin@freescale.com>
Signed-off-by: Haiying Wang <Haiying.Wang@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>