pinctrl: sh-pfc: r8a77990: Add DU pins, groups and function

This patch adds DU pins, groups and function for the R8A77990 (E3) SoC.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>