Supports boot up from NAND flash with software ECC eanbled.
And supports boot up from SD/MMC card with FAT file system.

As the boot from SD/MMC card with FAT file system, the BSS
segment is too big to fit into SRAM, so, use the lds to put
it into SDRAM.
Signed-off-by: NBo Shen <voice.shen@atmel.com>