kbuild: Enable DT symbols when CONFIG_OF_OVERLAY is used

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Replacement for "ARM: DT: Enable symbols when CONFIG_OF_OVERLAY is
used".

Author: geertu

scripts/Makefile.lib

@@ -388,6 +388,10 @@ $(obj)/%.dtb.S: $(obj)/%.dtb FORCE
 $(obj)/%.dtbo.S: $(obj)/%.dtbo FORCE
 	$(call if_changed,wrap_S_dtb)
 
+ifeq ($(CONFIG_OF_OVERLAY),y)
+DTC_FLAGS += -@
+endif
+
 quiet_cmd_dtc = DTC     $@
 cmd_dtc = $(HOSTCC) -E $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
 	$(DTC) -o $@ -b 0 \