dts/upstream: Add Makefile for MIPS

It is required to make OF_UPSTREAM work.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Reviewed-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>

dts/upstream/src/mips/Makefile

@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0+
+
+include $(srctree)/scripts/Makefile.dts
+
+targets += $(dtb-y)
+
+# Add any required device tree compiler flags here
+DTC_FLAGS += -a 0x8
+
+PHONY += dtbs
+dtbs: $(addprefix $(obj)/, $(dtb-y))
+	@:
+
+clean-files := */*.dtb */*.dtbo