kbuild: add dtc as dependency on .dtb files

If dtc is rebuilt, we should rebuild .dtb files with the new dtc.
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Rob Herring <robh@kernel.org>

scripts/Makefile.lib

@@ -316,7 +316,7 @@ cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
 		-d $(depfile).dtc.tmp $(dtc-tmp) ; \
 	cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)
 
-$(obj)/%.dtb: $(src)/%.dts FORCE
+$(obj)/%.dtb: $(src)/%.dts $(DTC) FORCE
 	$(call if_changed_dep,dtc)
 
 dtc-tmp = $(subst $(comma),_,$(dot-target).dts.tmp)