ARM: atmel: sama5d4ek: enable SPL support

The sama5d4ek support boot up from NAND flash, SD/MMC card and
also the SPI flash.

Signed-off-by: Bo Shen <voice.shen@atmel.com>
diff --git a/configs/sama5d4ek_nandflash_defconfig b/configs/sama5d4ek_nandflash_defconfig
index 8b7fbc3..d430fa7 100644
--- a/configs/sama5d4ek_nandflash_defconfig
+++ b/configs/sama5d4ek_nandflash_defconfig
@@ -1,3 +1,4 @@
+CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SAMA5D4,SYS_USE_NANDFLASH"
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_SAMA5D4EK=y