dt-bindings: pinctrl: rzn1: Convert to json-schema

Convert the Renesas RZ/N1 Pin controller Device Tree binding
documentation to json-schema.

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>
Tested-by: Gareth Williams <gareth.williams.jx@renesas.com>
Reviewed-by: Gareth Williams <gareth.williams.jx@renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200821112059.5133-1-geert+renesas@glider.be