dt-bindings: Pass binding directory to validation tools

In order to have $ref's to schema files within the kernel, we need to
pass the base path of bindings to the schema validation tools.

Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: devicetree@vger.kernel.org
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/Makefile

@@ -5,7 +5,7 @@ DT_MK_SCHEMA ?= dt-mk-schema
 DT_MK_SCHEMA_FLAGS := $(if $(DT_SCHEMA_FILES), -u)
 
 quiet_cmd_chk_binding = CHKDT   $(patsubst $(srctree)/%,%,$<)
-      cmd_chk_binding = $(DT_DOC_CHECKER) $< ; \
+      cmd_chk_binding = $(DT_DOC_CHECKER) -u $(srctree)/$(src) $< ; \
                         $(DT_EXTRACT_EX) $< > $@
 
 $(obj)/%.example.dts: $(src)/%.yaml FORCE