board: atmel: sama5d2_xplained: add SPL support

The sama5d2 Xplained SPL supports the boot medias: spi flash
and SD Card.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Andreas Bießmann <andreas.devel@googlemail.com>
diff --git a/configs/sama5d2_xplained_spiflash_defconfig b/configs/sama5d2_xplained_spiflash_defconfig
index 0271e8e..6d61a7e 100644
--- a/configs/sama5d2_xplained_spiflash_defconfig
+++ b/configs/sama5d2_xplained_spiflash_defconfig
@@ -1,6 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_AT91=y
 CONFIG_TARGET_SAMA5D2_XPLAINED=y
+CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="SAMA5D2,SYS_USE_SERIALFLASH"
 # CONFIG_CMD_IMI is not set
 # CONFIG_CMD_IMLS is not set