arm: xenguest_arm64: Add a empty devicetree file

Add an empty version of this file, so that we can at least build this
board when devicetrees are required.

The real devicetree is created by the Xen project on-the-fly.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/dts/Makefile b/arch/arm/dts/Makefile
index d53bae2..f634598 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -1140,6 +1140,8 @@
 	mt8516-pumpkin.dtb \
 	mt8518-ap1-emmc.dtb
 
+dtb-$(CONFIG_XEN) += xenguest-arm64.dtb
+
 dtb-$(CONFIG_TARGET_GE_BX50V3) += \
 	imx6q-bx50v3.dtb \
 	imx6q-b850v3.dtb \