dt-bindings: display: convert kingdisplay,kd035g6-54nt to DT Schema

v2:
  - Drop use of spi-slave.yaml (Maxime)
  - Introduce unevaluatedProperties (Maxime)
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Paul Cercueil <paul@crapouillou.net>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408195109.32692-14-sam@ravnborg.org

Documentation/devicetree/bindings/display/panel/kingdisplay,kd035g6-54nt.txt

-King Display KD035G6-54NT 3.5" (320x240 pixels) 24-bit TFT LCD panel
-
-Required properties:
-- compatible: should be "kingdisplay,kd035g6-54nt"
-- power-supply: See panel-common.txt
-- reset-gpios: See panel-common.txt
-
-Optional properties:
-- backlight: see panel-common.txt
-
-The generic bindings for the SPI slaves documented in [1] also apply.
-
-The device node can contain one 'port' child node with one child
-'endpoint' node, according to the bindings defined in [2]. This
-node should describe panel's video bus.
-
-[1]: Documentation/devicetree/bindings/spi/spi-bus.txt
-[2]: Documentation/devicetree/bindings/graph.txt
-
-Example:
-
-&spi {
-	panel@0 {
-		compatible = "kingdisplay,kd035g6-54nt";
-		reg = <0>;
-
-		spi-max-frequency = <3125000>;
-		spi-3wire;
-		spi-cs-high;
-
-		reset-gpios = <&gpe 2 GPIO_ACTIVE_LOW>;
-
-		backlight = <&backlight>;
-		power-supply = <&ldo6>;
-
-		port {
-			panel_input: endpoint {
-				remote-endpoint = <&panel_output>;
-			};
-		};
-	};
-};

Documentation/devicetree/bindings/display/panel/kingdisplay,kd035g6-54nt.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/kingdisplay,kd035g6-54nt.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: King Display KD035G6-54NT 3.5" (320x240 pixels) 24-bit TFT LCD panel
+
+description: |
+  The panel must obey the rules for a SPI slave device as specified in
+  spi/spi-controller.yaml
+
+maintainers:
+  - Paul Cercueil <paul@crapouillou.net>
+
+allOf:
+  - $ref: panel-common.yaml#
+
+properties:
+  compatible:
+    const: kingdisplay,kd035g6-54nt
+
+  backlight: true
+  port: true
+  power-supply: true
+  reg: true
+  reset-gpios: true
+
+required:
+  - compatible
+  - power-supply
+  - reset-gpios
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        panel@0 {
+            compatible = "kingdisplay,kd035g6-54nt";
+            reg = <0>;
+
+            spi-max-frequency = <3125000>;
+            spi-3wire;
+            spi-cs-high;
+
+            reset-gpios = <&gpe 2 GPIO_ACTIVE_LOW>;
+
+            backlight = <&backlight>;
+            power-supply = <&ldo6>;
+
+            port {
+                panel_input: endpoint {
+                    remote-endpoint = <&panel_output>;
+                };
+            };
+        };
+    };
+
+...