drm: rcar-du: Add r8a774c0 device support

Add support for the RZ/G2E (R8A774C0) SoC to the R-Car DU driver.

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>