kbuild: pass dst= to Makefile.headersinst from top Makefile

We can always pass dst= from the top Makefile.  This will simplify
the logic in Makefile.headersinst.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Makefile

@@ -1154,7 +1154,7 @@ PHONY += headers_install
 headers_install: __headers
 	$(if $(wildcard $(srctree)/arch/$(hdr-arch)/include/uapi/asm/Kbuild),, \
 	  $(error Headers not exportable for the $(SRCARCH) architecture))
-	$(Q)$(MAKE) $(hdr-inst)=include/uapi
+	$(Q)$(MAKE) $(hdr-inst)=include/uapi dst=include
 	$(Q)$(MAKE) $(hdr-inst)=arch/$(hdr-arch)/include/uapi $(hdr-dst)
 
 PHONY += headers_check_all
@@ -1163,7 +1163,7 @@ headers_check_all: headers_install_all
 
 PHONY += headers_check
 headers_check: headers_install
-	$(Q)$(MAKE) $(hdr-inst)=include/uapi HDRCHECK=1
+	$(Q)$(MAKE) $(hdr-inst)=include/uapi dst=include HDRCHECK=1
 	$(Q)$(MAKE) $(hdr-inst)=arch/$(hdr-arch)/include/uapi $(hdr-dst) HDRCHECK=1
 
 # ---------------------------------------------------------------------------

scripts/Makefile.headersinst

@@ -23,15 +23,12 @@ subdirs       := $(patsubst $(srcdir)/%/,%,\
 		 $(filter-out $(srcdir)/,\
 		 $(sort $(dir $(wildcard $(srcdir)/*/)))))
 
-# caller may set destination dir (when installing to asm/)
-_dst          := $(if $(dst),$(dst),$(obj))
-
 # Recursion
 __headers: $(subdirs)
 
 .PHONY: $(subdirs)
 $(subdirs):
-	$(Q)$(MAKE) $(hdr-inst)=$(obj)/$@ dst=$(_dst)/$@
+	$(Q)$(MAKE) $(hdr-inst)=$(obj)/$@ dst=$(dst)/$@
 
 # Skip header install/check for include/uapi and arch/$(hdr-arch)/include/uapi.
 # We have only sub-directories there.
@@ -48,8 +45,7 @@ ifneq ($(wildcard $(old-kbuild-file)),)
 include $(old-kbuild-file)
 endif
 
-installdir    := $(INSTALL_HDR_PATH)/$(subst uapi/,,$(_dst))
-
+installdir    := $(INSTALL_HDR_PATH)/$(dst)
 gendir        := $(objtree)/$(subst include/,include/generated/,$(obj))
 header-files  := $(notdir $(wildcard $(srcdir)/*.h))
 header-files  += $(notdir $(wildcard $(srcdir)/*.agh))