board/b4qds:Add support of 2 stage NAND boot-loader

board/b4qds:Add support of 2 stage NAND boot-loader

Add support of 2 stage NAND boot loader using SPL framework.
here, PBL initialise the internal SRAM and copy SPL(160KB). This further
initialise DDR using SPD and environment and copy u-boot(768 KB) from NAND to DDR.
Finally SPL transer control to u-boot.

Initialise/create followings required for SPL framework
  - Add spl.c which defines board_init_f, board_init_r
  - update tlb and ddr accordingly

Signed-off-by: Prabhakar Kushwaha <[email protected]>
Reviewed-by: York Sun <[email protected]>