devicetree/bindings: display: bridge: Add LVDS encoder DT bindings

The DT bindings support parallel to LVDS encoders that don't require any
configuration, similarly to the dumb VGA DAC DT bindings.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170302104728.7150-2-laurent.pinchart+renesas@ideasonboard.com