dt-bindings: pinctrl: renesas,rza2: Use 'additionalProperties' for child nodes

dt-bindings: pinctrl: renesas,rza2: Use 'additionalProperties' for child nodes

A schema under 'additionalProperties' works better for matching any
property/node other than the ones explicitly listed. Convert the schema
to use that rather than the wildcard and if/then schema.

Drop 'phandle' properties which never need to be explicitly listed while
we're here.

Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230819010928.916438-1-robh@kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>