drm: rcar-du: Add r8a77990 and r8a77995 device support

Add support for the R-Car D3 (R8A77995) and E3 (R8A77990) SoCs to the
R-Car DU driver. The two SoCs instantiate compatible DUs, so a single
information structure is enough.

Signed-off-by: Ulrich Hecht <uli+renesas@fpond.eu>
[Add support for R8A77990]
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>