dts, arm/arm64: Remove dtbs build rules in sub-makes

Add dtb files to build targets and let kbuild handle them. Thus,
special dtbs rules can be removed. This eases Makefiles and the
implementation of the support of vendor dtb subdirectories.

Signed-off-by: Robert Richter <rrichter@cavium.com>

arch/arm/Makefile

@@ -314,7 +314,7 @@ $(INSTALL_TARGETS):
 PHONY += dtbs dtbs_install
 
 dtbs: prepare scripts
-	$(Q)$(MAKE) $(build)=$(boot)/dts MACHINE=$(MACHINE) $@
+	$(Q)$(MAKE) $(build)=$(boot)/dts MACHINE=$(MACHINE)
 
 dtbs_install:
 	$(Q)$(MAKE) $(dtbinst)=$(boot)/dts MACHINE=$(MACHINE)

arch/arm/boot/dts/Makefile

@@ -517,13 +517,7 @@ dtb-$(CONFIG_MACH_DOVE) += dove-cm-a510.dtb \
 	dove-dove-db.dtb
 dtb-$(CONFIG_ARCH_MEDIATEK) += mt6589-aquaris5.dtb
 
-targets += dtbs dtbs_install
-targets += $(dtb-y)
 endif
 
-# *.dtb used to be generated in the directory above. Clean out the
-# old build results so people don't accidentally use them.
-dtbs: $(addprefix $(obj)/, $(dtb-y))
-	$(Q)rm -f $(obj)/../*.dtb
-
+always		:= $(dtb-y)
 clean-files	:= *.dtb

arch/arm64/Makefile

@@ -73,7 +73,7 @@ zinstall install: vmlinux
 PHONY += dtbs dtbs_install
 
 dtbs: prepare scripts
-	$(Q)$(MAKE) $(build)=$(boot)/dts $@
+	$(Q)$(MAKE) $(build)=$(boot)/dts
 
 dtbs_install:
 	$(Q)$(MAKE) $(dtbinst)=$(boot)/dts

arch/arm64/boot/dts/Makefile

@@ -2,9 +2,5 @@ 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
 
-targets += dtbs dtbs_install
-targets += $(dtb-y)
-
-dtbs: $(addprefix $(obj)/, $(dtb-y))
-
+always		:= $(dtb-y)
 clean-files	:= *.dtb