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/arch/arm/mach-at91/Kconfig b/arch/arm/mach-at91/Kconfig
index c333647..9426302b 100644
--- a/arch/arm/mach-at91/Kconfig
+++ b/arch/arm/mach-at91/Kconfig
@@ -74,6 +74,7 @@
 config TARGET_SAMA5D2_XPLAINED
 	bool "SAMA5D2 Xplained board"
 	select CPU_V7
+	select SUPPORT_SPL
 
 config TARGET_SAMA5D3_XPLAINED
 	bool "SAMA5D3 Xplained board"