pinctrl: sh-pfc: Add r8a77470 PFC support

Add PFC support for the R8A77470 SoC including pin groups for
some on-chip devices such as SCIF and MMC.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>