kbuild: determine the output format of DTC by the target suffix

cmd_dtc takes the additional parameter $(2) to select the target
format, dtb or yaml. This makes things complicated when it is used
with cmd_and_fixdep and if_changed_rule. I actually stumbled on this.
See commit 3d4b2238 ("kbuild: fix DT binding schema rule again to
avoid needless rebuilds").

Extract the suffix part of the target instead of passing the parameter.
Fortunately, this works for both $(obj)/%.dtb and $(obj)/%.dt.yaml .
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.lib

@@ -287,13 +287,13 @@ $(obj)/%.dtb.S: $(obj)/%.dtb FORCE
 quiet_cmd_dtc = DTC     $@
 cmd_dtc = mkdir -p $(dir ${dtc-tmp}) ; \
 	$(HOSTCC) -E $(dtc_cpp_flags) -x assembler-with-cpp -o $(dtc-tmp) $< ; \
-	$(DTC) -O $(2) -o $@ -b 0 \
+	$(DTC) -O $(patsubst .%,%,$(suffix $@)) -o $@ -b 0 \
 		$(addprefix -i,$(dir $<) $(DTC_INCLUDE)) $(DTC_FLAGS) \
 		-d $(depfile).dtc.tmp $(dtc-tmp) ; \
 	cat $(depfile).pre.tmp $(depfile).dtc.tmp > $(depfile)
 
 $(obj)/%.dtb: $(src)/%.dts $(DTC) FORCE
-	$(call if_changed_dep,dtc,dtb)
+	$(call if_changed_dep,dtc)
 
 DT_CHECKER ?= dt-validate
 DT_BINDING_DIR := Documentation/devicetree/bindings
@@ -304,7 +304,7 @@ quiet_cmd_dtb_check =	CHECK   $@
       cmd_dtb_check =	$(DT_CHECKER) -u $(srctree)/$(DT_BINDING_DIR) -p $(DT_TMP_SCHEMA) $@
 
 define rule_dtc
-	$(call cmd_and_fixdep,dtc,yaml)
+	$(call cmd_and_fixdep,dtc)
 	$(call cmd,dtb_check)
 endef