imx6: dts: add wandboard dtb target to fix build error

Fix broken build:
Device Tree Source is not correctly specified.
Please define 'CONFIG_DEFAULT_DEVICE_TREE'
or build with 'DEVICE_TREE=<device_tree>' argument

Signed-off-by: Anatolij Gustschin <agust@denx.de>
diff --git a/arch/arm/dts/Makefile b/arch/arm/dts/Makefile
index 0fb6419..0aee8df 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -522,6 +522,9 @@
 	imx6qp-sabreauto.dtb \
 	imx6qp-sabresd.dtb
 
+dtb-$(CONFIG_TARGET_WANDBOARD) += \
+	imx6dl-wandboard-revb1.dtb
+
 dtb-$(CONFIG_MX6SL) += imx6sl-evk.dtb
 
 dtb-$(CONFIG_MX6SLL) += imx6sll-evk.dtb