dtc: enable generation of symbols

PD#173147: update dtc to v1.4.4

add -@ to dtc option to enable generation of symbols

Change-Id: Ica497de494a3f228f4111773d9cba674b2a2e061
Signed-off-by: Jianxin Pan <jianxin.pan@amlogic.com>

scripts/Makefile.lib

@@ -314,7 +314,7 @@ $(obj)/%.dtb.S: $(obj)/%.dtb
 quiet_cmd_dtc = DTC     $@
 cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
 	$(CPP) $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
-	$(DTC) -O dtb -o $@ -b 0 \
+	$(DTC) -@ -O dtb -o $@ -b 0 \
 		-i $(dir $<) $(DTC_FLAGS) \
 		-d $(depfile).dtc.tmp $(dtc-tmp) ; \
 	cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)