arm64: dts: renesas: r8a77965: Add LVDS support

The M3-N (r8a77965) platform has one LVDS encoder connected to the DU.
Add the corresponding DT node and wire it up.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>