ARM: at91: dt: add dts file for sama5d3 Xplained

Add the device tree file for sama5d3 Xplained board.

The dts files are copied from the Linux-4.9, do changes as below.
 - add the "u-boot,dm-pre-reloc" property to determine which nodes
   which are needed by SPL and by the board_init_f stage.
 - fix the compile warning.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
diff --git a/arch/arm/dts/Makefile b/arch/arm/dts/Makefile
index e7ccb53..c131149 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -355,6 +355,9 @@
 	sama5d36ek.dtb \
 	sama5d36ek_cmp.dtb
 
+dtb-$(CONFIG_TARGET_SAMA5D3_XPLAINED) += \
+	at91-sama5d3_xplained.dtb
+
 dtb-$(CONFIG_ARCH_BCM283X) += \
 	bcm2835-rpi-a-plus.dtb \
 	bcm2835-rpi-a.dtb \