drm: rcar-du: lvds: Add r8a7744 support

The LVDS encoders on RZ/G1N SoC is similar to RZ/G1M. Add support for
RZ/G1N (R8A7744) SoC to the LVDS encoder driver.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>