pinctrl: sh-pfc: Initial R8A7796 PFC support

This patch adds initial pinctrl driver to support for the R8A7796 SoC.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[uli: rebased on top of renesas-drivers]
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>