dts, arm64: Move dts files to vendor subdirs

Moving dts files to vendor subdirs.
Acked-by: NRob Herring <robh@kernel.org>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: NRobert Richter <rrichter@cavium.com>

arch/arm64/boot/dts/Makefile

-dtb-$(CONFIG_ARCH_THUNDER) += thunder-88xx.dtb
-dtb-$(CONFIG_ARCH_VEXPRESS) += rtsm_ve-aemv8a.dtb foundation-v8.dtb
-dtb-$(CONFIG_ARCH_XGENE) += apm-mustang.dtb
+dts-dirs += apm
+dts-dirs += arm
+dts-dirs += cavium
 
 always		:= $(dtb-y)
 subdir-y	:= $(dts-dirs)

arch/arm64/boot/dts/apm/Makefile

+dtb-$(CONFIG_ARCH_XGENE) += apm-mustang.dtb
+
+always		:= $(dtb-y)
+subdir-y	:= $(dts-dirs)
+clean-files	:= *.dtb

arch/arm64/boot/dts/arm/Makefile

+dtb-$(CONFIG_ARCH_VEXPRESS) += foundation-v8.dtb
+dtb-$(CONFIG_ARCH_VEXPRESS) += rtsm_ve-aemv8a.dtb
+
+always		:= $(dtb-y)
+subdir-y	:= $(dts-dirs)
+clean-files	:= *.dtb

arch/arm64/boot/dts/cavium/Makefile

+dtb-$(CONFIG_ARCH_THUNDER) += thunder-88xx.dtb
+
+always		:= $(dtb-y)
+subdir-y	:= $(dts-dirs)
+clean-files	:= *.dtb