ARM: dts: r8a7791: Convert to new LVDS DT bindings

The internal LVDS encoder now has DT bindings separate from the DU. Port
the device tree over to the new model.

Fixes: c6a27fa4 ("drm: rcar-du: Convert LVDS encoder code to bridge driver")
Fixes: bb21803e ("ARM: dts: r8a7791: add soc node")
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>