ARM: atmel: sama5d4_xplained: enable spl support

Signed-off-by: Bo Shen <voice.shen@atmel.com>
diff --git a/configs/sama5d4_xplained_mmc_defconfig b/configs/sama5d4_xplained_mmc_defconfig
index 3720f3c..73df28c 100644
--- a/configs/sama5d4_xplained_mmc_defconfig
+++ b/configs/sama5d4_xplained_mmc_defconfig
@@ -1,3 +1,4 @@
+CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SAMA5D4,SYS_USE_MMC"
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_SAMA5D4_XPLAINED=y