dt-bindings: display: Document FriendlyELEC HD702E LCD panel

HD702E lcd is FriendlyELEC developed eDP LCD panel with 800x1280
resolution. It has built in Goodix, GT9271 captive touchscreen
with backlight adjustable via PWM.

Add dt-bindings documentation for it.
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190507130708.11255-1-jagan@amarulasolutions.com

Documentation/devicetree/bindings/display/panel/friendlyarm,hd702e.txt

+FriendlyELEC HD702E 800x1280 LCD panel
+
+HD702E lcd is FriendlyELEC developed eDP LCD panel with 800x1280
+resolution. It has built in Goodix, GT9271 captive touchscreen
+with backlight adjustable via PWM.
+
+Required properties:
+- compatible: should be "friendlyarm,hd702e"
+- power-supply: regulator to provide the supply voltage
+
+Optional properties:
+- backlight: phandle of the backlight device attached to the panel
+
+Optional nodes:
+- Video port for LCD panel input.
+
+This binding is compatible with the simple-panel binding, which is specified
+in simple-panel.txt in this directory.
+
+Example:
+
+	panel {
+		compatible ="friendlyarm,hd702e", "simple-panel";
+		backlight = <&backlight>;
+		power-supply = <&vcc3v3_sys>;
+
+		port {
+			panel_in_edp: endpoint {
+				remote-endpoint = <&edp_out_panel>;
+			};
+		};
+	};