kbuild: check libyaml installation for 'make dt_binding_check'

If you run 'make dtbs_check' without installing the libyaml package,
the error message "dtc needs libyaml ..." is shown.

This should be checked also for 'make dt_binding_check' because dtc
needs to validate *.example.dts extracted from *.yaml files.

It is missing since commit 4f0e3a57d6 ("kbuild: Add support for DT
binding schema checks"), but this fix-up is applicable only after commit
e10c4321dc ("kbuild: allow to run dt_binding_check and dtbs_check
in a single command").

I gave the Fixes tag to the latter in case somebody is interested in
back-porting this.

Fixes: e10c4321dc ("kbuild: allow to run dt_binding_check and dtbs_check in a single command")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

scripts/dtc/Makefile

@@ -13,7 +13,7 @@ dtc-objs	+= dtc-lexer.lex.o dtc-parser.tab.o
 HOST_EXTRACFLAGS := -I $(srctree)/$(src)/libfdt
 
 ifeq ($(shell pkg-config --exists yaml-0.1 2>/dev/null && echo yes),)
-ifneq ($(CHECK_DTBS),)
+ifneq ($(CHECK_DT_BINDING)$(CHECK_DTBS),)
 $(error dtc needs libyaml for DT schema validation support. \
 	Install the necessary libyaml development package.)
 endif