dt-bindings: pinctrl: rza1: Convert to json-schema

Convert the Renesas RZ/A1 combined Pin and GPIO controller Device Tree
binding documentation to json-schema.

Rename "rza1-pinctrl" to "rza1-ports", to match the compatible value
scheme.
Use "pinctrl" generic node name.
Drop generic and consumer examples, as they do not belong here.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200821111956.4989-1-geert+renesas@glider.be