dt-bindings: pinctrl: sh-pfc: Document r8a7742 PFC support

Document PFC support for the RZ/G1H (R8A7742) SoC.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marian-Cristian Rotariu <marian-cristian.rotariu.rb@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1588542414-14826-2-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com


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