dt-bindings: pinctrl: renesas: Document RZ/G2UL pinctrl

Document Renesas RZ/G2UL pinctrl bindings. RZ/G2UL GPIO block is
almost identical to RZ/G2L and has lesser pins compared to RZ/G2L.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220315152717.20045-1-biju.das.jz@bp.renesas.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>