pinctrl: sh-pfc: r8a77990: Add PWM pins, groups and functions

This patch adds PWM{0,1,2,3,4,5,6} pins, groups and functions to
the R8A77990 SoC.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>