drm: rcar-du: Add r8a77980 support

Add direct support for the r8a77980 (V3H).

The V3H shares a common, compatible configuration with the r8a77970
(V3M) so that device info structure is reused.

Signed-off-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>