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