pinctrl: sh-pfc: Add r8a7793 support

Regarding pin control, r8a7791 and r8a7793 are identical, so it is
sufficient to add an sh_pfc_soc_info structure to enable r8a7793 support.

Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>