dt-bindings: display: panel: Add binding document for Leadtek LTK500HD1829

The LTK500HD1829 is a 5.0" 720x1280 DSI display.

v3:
  - fixed example by adding address,size-cells (sam)

changes in v2:
- fix id (Maxime)
- drop port (Maxime)
Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191224112641.30647-2-heiko@sntech.de

Documentation/devicetree/bindings/display/panel/leadtek,ltk500hd1829.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/leadtek,ltk500hd1829.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Leadtek LTK500HD1829 5.0in 720x1280 DSI panel
+
+maintainers:
+  - Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
+
+allOf:
+  - $ref: panel-common.yaml#
+
+properties:
+  compatible:
+    const: leadtek,ltk500hd1829
+  reg: true
+  backlight: true
+  reset-gpios: true
+  iovcc-supply:
+     description: regulator that supplies the iovcc voltage
+  vcc-supply:
+     description: regulator that supplies the vcc voltage
+
+required:
+  - compatible
+  - reg
+  - backlight
+  - iovcc-supply
+  - vcc-supply
+
+additionalProperties: false
+
+examples:
+  - |
+    dsi@ff450000 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+        panel@0 {
+            compatible = "leadtek,ltk500hd1829";
+            reg = <0>;
+            backlight = <&backlight>;
+            iovcc-supply = <&vcc_1v8>;
+            vcc-supply = <&vcc_2v8>;
+        };
+    };
+
+...