dt-bindings: Turn on undocumented compatible checks

The undocumented compatibles in the examples are down to just a few
left. Turn on the warning by default. The increased visibility should
get the remaining warnings fixed.
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231128221008.4050638-2-robh@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/Makefile

@@ -61,9 +61,6 @@ override DTC_FLAGS := \
 	-Wno-unique_unit_address \
 	-Wunique_unit_address_if_enabled
 
-# Disable undocumented compatible checks until warning free
-override DT_CHECKER_FLAGS ?=
-
 $(obj)/processed-schema.json: $(DT_DOCS) $(src)/.yamllint check_dtschema_version FORCE
 	$(call if_changed_rule,chkdt)