powerpc/dts: Makefile changes to clean and build dts

Signed-off-by: Jagdish Gediya <jagdish.gediya@nxp.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: York Sun <york.sun@nxp.com>
diff --git a/arch/powerpc/dts/Makefile b/arch/powerpc/dts/Makefile
new file mode 100644
index 0000000..de14e7b
--- /dev/null
+++ b/arch/powerpc/dts/Makefile
@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: GPL-2.0+
+
+targets += $(dtb-y)
+
+# Add any required device tree compiler flags here
+DTC_FLAGS +=
+
+PHONY += dtbs
+dtbs: $(addprefix $(obj)/, $(dtb-y))
+	@:
+
+clean-files := *.dtb