kmsro: Add 'rcar-du' driver support

kmsro: Add 'rcar-du' driver support

rcar-du is used by Renesas R-Car and RZ/G SOCs.
Driver is available in the mainline kernel [1]
[1] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/rcar-du

Suggested-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Show Liu <show.liu.yj@renesas.com>
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14393>