Enable SPL support for at91sam9n12ek boards, now it supports boot up from NAND flash, serial flash.
Signed-off-by: Bo Shen
CONFIG_SPL=y CONFIG_SYS_EXTRA_OPTIONS="AT91SAM9N12,SYS_USE_NANDFLASH" CONFIG_ARM=y CONFIG_ARCH_AT91=y CONFIG_TARGET_AT91SAM9N12EK=y
