pinctrl: sh-pfc: r8a7796: Add PWM pins, groups and functions

This patch adds PWM{0,1,2,3,4,5,6} pins, groups and functions to
R8A7796 SoC.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Ulrich Hecht <ulrich.hecht+renesas@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>