dt-bindings: display: Convert sgd,gktw70sdae4se panel to DT schema

Convert the sgd,gktw70sdae4se LVDS panel binding to DT schema.

Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190705164221.4462-14-robh@kernel.org