MIPS: Create common infrastructure for building built-in device-trees

In preparation for moving the device-trees to a common location,
introduce the config option BUILTIN_DTB, which can be selected by
platforms that use a device-tree built into the kernel image, and
create a Makefile to build the device-trees in arch/mips/boot/dts/.
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/7564/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -2482,6 +2482,9 @@ config USE_OF
 	select OF_EARLY_FLATTREE
 	select IRQ_DOMAIN
 
+config BUILTIN_DTB
+	bool
+
 endmenu
 
 config LOCKDEP_SUPPORT

arch/mips/Makefile

@@ -333,6 +333,12 @@ endif
 
 CLEAN_FILES += vmlinux.32 vmlinux.64
 
+# device-trees
+core-$(CONFIG_BUILTIN_DTB) += arch/mips/boot/dts/
+
+%.dtb %.dtb.S %.dtb.o: | scripts
+	$(Q)$(MAKE) $(build)=arch/mips/boot/dts arch/mips/boot/dts/$@
+
 archprepare:
 ifdef CONFIG_MIPS32_N32
 	@echo '  Checking missing-syscalls for N32'

arch/mips/boot/dts/Makefile

+obj-y		+= $(patsubst %.dtb, %.dtb.o, $(dtb-y))
+
+clean-files	+= *.dtb.S