dt-bindings: do not build processed-schema.yaml for 'make dt_binding_check'

Currently, processed-schema.yaml is always built, but it is actually
used only for 'make dtbs_check'.

'make dt_binding_check' uses processed-schema-example.yaml instead.

Build processed-schema.yaml only for 'make dtbs_check'.

Signed-off-by: Masahiro Yamada <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/Makefile

···
 $(obj)/processed-schema.yaml: $(DT_SCHEMA_FILES) check_dtschema_version FORCE
 	$(call if_changed,mk_schema)
 
-extra-y += processed-schema.yaml
+extra-$(CHECK_DTBS) += processed-schema.yaml
 
 # Hack: avoid 'Argument list too long' error for 'make clean'. Remove most of
 # build artifacts here before they are processed by scripts/Makefile.clean