pinctrl: sh-pfc: r8a7795: Add DU support

Only the DU parallel RGB output signals are included, HDMI and TCON pins
will be added in separate groups.

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