dt-bindings: pinctrl: Add missing additionalProperties on child node schemas

Just as unevaluatedProperties or additionalProperties are required at
the top level of schemas, they should (and will) also be required for
child node schemas. That ensures only documented properties are
present for any node.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230925212713.1975800-1-robh@kernel.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>