dt-bindings: display: bridge: Add binding for R-Car MIPI DSI/CSI-2 TX

The R-Car MIPI DSI/CSI-2 TX is embedded in the Renesas R-Car V3U SoC. It
can operate in either DSI or CSI-2 mode, with up to four data lanes.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>