dt-bindings: pinctrl: renesas,rzg2l-pinctrl: Document the properties to handle GPIO IRQ

Document the required properties to handle GPIO IRQ.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220707182314.66610-6-prabhakar.mahadev-lad.rj@bp.renesas.com