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>

arch/mips/Makefile

@@ -339,6 +339,10 @@ core-$(CONFIG_BUILTIN_DTB) += arch/mips/boot/dts/
 %.dtb %.dtb.S %.dtb.o: | scripts
 	$(Q)$(MAKE) $(build)=arch/mips/boot/dts arch/mips/boot/dts/$@
 
+PHONY += dtbs
+dtbs: scripts
+	$(Q)$(MAKE) $(build)=arch/mips/boot/dts dtbs
+
 archprepare:
 ifdef CONFIG_MIPS32_N32
 	@echo '  Checking missing-syscalls for N32'
@@ -373,6 +377,7 @@ define archhelp
 	echo '  vmlinuz.srec         - SREC zboot image'
 	echo '  uImage               - U-Boot image'
 	echo '  uImage.gz            - U-Boot image (gzip)'
+	echo '  dtbs                 - Device-tree blobs for enabled boards'
 	echo
 	echo '  These will be default as appropriate for a configured platform.'
 endef

arch/mips/boot/.gitignore

@@ -5,3 +5,4 @@ zImage
 zImage.tmp
 calc_vmlinuz_load_addr
 uImage
+*.dtb

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