dt-bindings: pinctrl: sh-pfc: Convert to json-schema

Convert the Renesas Pin Function Controller (PFC) Device Tree binding
documentation to json-schema.

Document missing properties.
Drop deprecated and obsolete #gpio-range-cells property.
Update the example to match reality.
Drop consumer examples, as they do not belong here.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20200821112208.5295-1-geert+renesas@glider.be