dt-bindings: drm/panel: simple: add sharp, lq070y3dg3b panel

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/ee90ed56d2c294ce8ac3b44bf2229c5ab9f85e91.1559905870.git.hns@goldelico.com

Documentation/devicetree/bindings/display/panel/sharp,lq070y3dg3b.txt

+Sharp LQ070Y3DG3B 7.0" WVGA landscape TFT LCD panel
+
+Required properties:
+- compatible: should be "sharp,lq070y3dg3b"
+
+Optional properties:
+- enable-gpios: GPIO pin to enable or disable the panel
+- backlight: phandle of the backlight device attached to the panel
+- power-supply: phandle of the regulator that provides the supply voltage
+
+This binding is compatible with the simple-panel binding, which is specified
+in simple-panel.txt in this directory.