pinctrl: sh-pfc: r8a7794: Add PWM[0123456] support

This patch adds PFC PWM[0123456] pin groups and functions, enabling
PWM on the r8a7794 and r8a7745.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Biju Das <biju.das@bp.renesas.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>