arm64: dts: renesas: r8a774c0: Point LVDS0 to its companion LVDS1

Add the new renesas,companion property to the LVDS0 node to point to the
companion LVDS encoder LVDS1.
Based on similar work from Laurent Pinchart for the r8a7799[05].

Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>