kbuild: take into account DT_SCHEMA_FILES changes while checking dtbs

It is useful to be able to recheck dtbs files against a limited set of
DT schema files. This can be accomplished by using differnt
DT_SCHEMA_FILES argument values while rerunning make dtbs_check. However
for some reason if_changed_rule doesn't pick up the rule_dtc changes
(and doesn't retrigger the build).

Fix this by changing if_changed_rule to if_changed_dep and squashing DTC
and dt-validate into a single new command. Then if_changed_dep triggers
on DT_SCHEMA_FILES changes and reruns the build/check.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20220915114422.79378-1-dmitry.baryshkov@linaro.org
Signed-off-by: Rob Herring <robh@kernel.org>

scripts/Makefile.lib

@@ -371,17 +371,15 @@ DT_CHECKER_FLAGS ?= $(if $(DT_SCHEMA_FILES),-l $(DT_SCHEMA_FILES),-m)
 DT_BINDING_DIR := Documentation/devicetree/bindings
 DT_TMP_SCHEMA := $(objtree)/$(DT_BINDING_DIR)/processed-schema.json
 
-quiet_cmd_dtb_check =	CHECK   $@
-      cmd_dtb_check =	$(DT_CHECKER) $(DT_CHECKER_FLAGS) -u $(srctree)/$(DT_BINDING_DIR) -p $(DT_TMP_SCHEMA) $@ || true
+quiet_cmd_dtb =	DTC_CHK $@
+      cmd_dtb =	$(cmd_dtc) ; $(DT_CHECKER) $(DT_CHECKER_FLAGS) -u $(srctree)/$(DT_BINDING_DIR) -p $(DT_TMP_SCHEMA) $@ || true
+else
+quiet_cmd_dtb = $(quiet_cmd_dtc)
+      cmd_dtb = $(cmd_dtc)
 endif
 
-define rule_dtc
-	$(call cmd_and_fixdep,dtc)
-	$(call cmd,dtb_check)
-endef
-
 $(obj)/%.dtb: $(src)/%.dts $(DTC) $(DT_TMP_SCHEMA) FORCE
-	$(call if_changed_rule,dtc)
+	$(call if_changed_dep,dtb)
 
 $(obj)/%.dtbo: $(src)/%.dts $(DTC) FORCE
 	$(call if_changed_dep,dtc)