kbuild: unify clean-dirs rule for in-kernel and external module

Factor out the duplicated code for in-kernel and external module
cleaning.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -1017,6 +1017,7 @@ vmlinux-alldirs	:= $(sort $(vmlinux-dirs) Documentation \
 			$(drivers-) $(net-) $(libs-) $(virt-))))
 
 build-dirs	:= $(vmlinux-dirs)
+clean-dirs	:= $(vmlinux-alldirs)
 
 init-y		:= $(patsubst %/, %/built-in.a, $(init-y))
 core-y		:= $(patsubst %/, %/built-in.a, $(core-y))
@@ -1388,11 +1389,8 @@ DISTCLEAN_FILES += tags TAGS cscope* GPATH GTAGS GRTAGS GSYMS
 #
 clean: rm-dirs  := $(CLEAN_DIRS)
 clean: rm-files := $(CLEAN_FILES)
-clean-dirs      := $(addprefix _clean_, $(vmlinux-alldirs))
 
-PHONY += $(clean-dirs) clean archclean vmlinuxclean
-$(clean-dirs):
-	$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
+PHONY += archclean vmlinuxclean
 
 vmlinuxclean:
 	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/link-vmlinux.sh clean
@@ -1629,12 +1627,7 @@ PHONY += _emodinst_post
 _emodinst_post: _emodinst_
 	$(call cmd,depmod)
 
-clean-dirs := $(addprefix _clean_,$(KBUILD_EXTMOD))
-
-PHONY += $(clean-dirs) clean
-$(clean-dirs):
-	$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
-
+clean-dirs := $(KBUILD_EXTMOD)
 clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers
 
 PHONY += /
@@ -1664,6 +1657,11 @@ descend: $(build-dirs)
 $(build-dirs): prepare
 	$(Q)$(MAKE) $(build)=$@ need-builtin=1 need-modorder=1
 
+clean-dirs := $(addprefix _clean_, $(clean-dirs))
+PHONY += $(clean-dirs) clean
+$(clean-dirs):
+	$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)
+
 clean: $(clean-dirs)
 	$(call cmd,rmdirs)
 	$(call cmd,rmfiles)