pinctrl: sh-pfc: r8a7795: Add PWM support

This patch adds PWM[0-6] pinmux support to r8a7795 SoC.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[uli: adapted to mainline PFC driver]
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>