dt-bindings: Add Logic PD Type 28 display panel

This patch adds documentation of device tree bindings for the WVGA panel
Logic PD Type 28 display.
Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191016135147.7743-2-aford173@gmail.com

Documentation/devicetree/bindings/display/panel/logicpd,type28.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/logicpd,type28.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Logic PD Type 28 4.3" WQVGA TFT LCD panel
+
+maintainers:
+  - Adam Ford <aford173@gmail.com>
+
+allOf:
+  - $ref: panel-common.yaml#
+
+properties:
+  compatible:
+    const: logicpd,type28
+
+  power-supply: true
+  enable-gpios: true
+  backlight: true
+  port: true
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    lcd0: display {
+      compatible = "logicpd,type28";
+      enable-gpios = <&gpio5 27 0>;
+      backlight = <&backlight>;
+      port {
+        lcd_in: endpoint {
+          remote-endpoint = <&dpi_out>;
+        };
+      };
+    };
+
+...