pinctrl: sh-pfc: r8a77965: Add DU RGB output pins, groups and functions

This patch adds pins, groups and functions for parallel RGB output
signals from DU. The HDMI and TCON pins are added to separate groups.

Based on a similar patch of the R8A7796 PFC driver by Niklas Söderlund
<niklas.soderlund+renesas@ragnatech.se>.

Signed-off-by: Takeshi Kihara <takeshi.kihara.df@renesas.com>
[Kieran: Rebase on top of tree]
Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>