Kbuild: standalone: do not ignore platform-specific OBJCOPYFLAGS

Currently the OBJCOPYFLAGS are cleared when assigning "-O srec"
or "-O binary" for standalone programs. All flags set by arch-specific
Makefiles are lost. This is bad if an arch demands arch-specific
flags for the objcopy step.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

examples/standalone/Makefile

@@ -62,11 +62,11 @@ quiet_cmd_link_elf = LD      $@
 $(ELF): $(obj)/%: $(obj)/%.o $(LIB) FORCE
 	$(call if_changed,link_elf)
 
-$(obj)/%.srec: OBJCOPYFLAGS := -O srec
+$(obj)/%.srec: OBJCOPYFLAGS += -O srec
 $(obj)/%.srec: $(obj)/% FORCE
 	$(call if_changed,objcopy)
 
-$(obj)/%.bin: OBJCOPYFLAGS := -O binary
+$(obj)/%.bin: OBJCOPYFLAGS += -O binary
 $(obj)/%.bin: $(obj)/% FORCE
 	$(call if_changed,objcopy)