powerpc/T4QDS: add two stage boot of nand/sd

Add support of 2 stage NAND/SD boot loader using SPL framework.
PBL initialise the internal SRAM and copy SPL, this further
initialise DDR using SPD and environment and copy u-boot from
NAND/SD to DDR, finally SPL transfer control to u-boot.
NOR uses CS1 instead of CS2 when NAND boot, fix it.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>