drm/rcar-du: dsi: Add r8a779h0 support

drm/rcar-du: dsi: Add r8a779h0 support

Add support for DSI on r8a779h0. As it is identical to DSI on r8a779g0,
all we need is to handle the compatible string.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241217-rcar-gh-dsi-v5-6-e77421093c05@ideasonboard.com