dt-bindings: drm/panel: Document Innolux TV123WAM panel bindings

Innolux TV123WAM is a 12.3" eDP display panel with
2160x1440 resolution, which can be supported by simple
panel driver.

Changes in v1:
 - Make use of simple panel driver instead of creating
   a new driver for this panel (Sean Paul).
 - Combine dt-binding and driver changes into one patch
   as done by other existing panel support changes.

Changes in v2:
 - Separate driver change from dt-binding documentation (Rob Herring).
 - Add the properties from simple-panel binding that are applicable to
   this panel (Rob Herring).
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1526363564-13823-5-git-send-email-spanda@codeaurora.org

Documentation/devicetree/bindings/display/panel/innolux,tv123wam.txt

+Innolux TV123WAM 12.3 inch eDP 2K display panel
+
+This binding is compatible with the simple-panel binding, which is specified
+in simple-panel.txt in this directory.
+
+Required properties:
+- compatible: should be "innolux,tv123wam"
+- power-supply: regulator to provide the supply voltage
+
+Optional properties:
+- enable-gpios: GPIO pin to enable or disable the panel
+- backlight: phandle of the backlight device attached to the panel
+
+Example:
+	panel_edp: panel-edp {
+		compatible = "innolux,tv123wam";
+		enable-gpios = <&msmgpio 31 GPIO_ACTIVE_LOW>;
+		power-supply = <&pm8916_l2>;
+		backlight = <&backlight>;
+	};