drm: rcar-du: lvds: Add R8A77965 support

Add support for the R-Car M3-N (R8A77965) SoC to the LVDS encoder
driver. The encoder appears identical to the M3-W version, we can thus
simply point to the generic Gen3 data.

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