kbuild: add FORCE to dependency of $(obj)/dts/dt-platdata.o

if_changed must have FORCE as a prerequisite.

Add $(obj)/dts/dt-platdata.o to 'targets' so that the corresponding
.cmd file is included.
Signed-off-by: NMasahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.spl

@@ -307,10 +307,11 @@ quiet_cmd_dtoch = DTOC H  $@
 cmd_dtoch = $(pythonpath) $(srctree)/tools/dtoc/dtoc -d $(obj)/$(SPL_BIN).dtb -o $@ struct
 
 quiet_cmd_plat = PLAT    $@
-cmd_plat = $(CC) $(c_flags) -c $< -o $@
+cmd_plat = $(CC) $(c_flags) -c $< -o $(filter-out $(PHONY),$@)
 
+targets += $(obj)/dts/dt-platdata.o
 $(obj)/dts/dt-platdata.o: $(obj)/dts/dt-platdata.c \
-		include/generated/dt-structs-gen.h
+		include/generated/dt-structs-gen.h FORCE
 	$(call if_changed,plat)
 
 PHONY += dts_dir