MIPS: Add support for building device-tree binaries

Add a 'dtbs' Makefile target that just builds the device-tree binaries
enabled by the configuration.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: David Daney <david.daney@cavium.com>
Cc: John Crispin <blogic@openwrt.org>
Cc: Jayachandran C <jchandra@broadcom.com>
Cc: Qais Yousef <qais.yousef@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7557/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/boot/dts/Makefile b/arch/mips/boot/dts/Makefile
index 6bb41df..9b3da1f 100644
--- a/arch/mips/boot/dts/Makefile
+++ b/arch/mips/boot/dts/Makefile
@@ -1,3 +1,8 @@
 obj-y		+= $(patsubst %.dtb, %.dtb.o, $(dtb-y))
 
-clean-files	+= *.dtb.S
+targets		+= dtbs
+targets		+= $(dtb-y)
+
+dtbs: $(addprefix $(obj)/, $(dtb-y))
+
+clean-files	+= *.dtb *.dtb.S