csky: use common dtb build rules

Remove the Kbuild rules in arch/csky and use common dtb build rules.

This modification is based on:

commit 37c8a5fa ("kbuild: consolidate Devicetree dtb build rules")
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>

arch/csky/Makefile

@@ -69,20 +69,11 @@ core-y += $(boot)/dts/
 
 all: zImage
 
-
-dtbs: scripts
-	$(Q)$(MAKE) $(build)=$(boot)/dts
-
-%.dtb %.dtb.S %.dtb.o: scripts
-	$(Q)$(MAKE) $(build)=$(boot)/dts $(boot)/dts/$@
-
-zImage Image uImage: vmlinux dtbs
+zImage Image uImage: vmlinux
 	$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
 
 archclean:
 	$(Q)$(MAKE) $(clean)=$(boot)
-	$(Q)$(MAKE) $(clean)=$(boot)/dts
-	rm -rf arch/csky/include/generated
 
 define archhelp
   echo  '* zImage       - Compressed kernel image (arch/$(ARCH)/boot/zImage)'

arch/csky/boot/dts/Makefile

 dtstree	:= $(srctree)/$(src)
 
 dtb-y := $(patsubst $(dtstree)/%.dts,%.dtb, $(wildcard $(dtstree)/*.dts))
-
-always += $(dtb-y)
-clean-files += *.dtb *.dtb.S