drm/panel: Add DT bindings for Sony ACX424AKP

This adds device tree bindings for the Sony ACX424AKP panel.
Let's use YAML.

Cc: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191114131525.3988-1-linus.walleij@linaro.org

Documentation/devicetree/bindings/display/panel/sony,acx424akp.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/sony,acx424akp.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Sony ACX424AKP 4" 480x864 AMOLED panel
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+allOf:
+  - $ref: panel-common.yaml#
+
+properties:
+  compatible:
+    const: sony,acx424akp
+  reg: true
+  reset-gpios: true
+  vddi-supply:
+     description: regulator that supplies the vddi voltage
+  enforce-video-mode: true
+
+required:
+  - compatible
+  - reg
+  - reset-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    dsi-controller@a0351000 {
+        compatible = "ste,mcde-dsi";
+        reg = <0xa0351000 0x1000>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        panel@0 {
+            compatible = "sony,acx424akp";
+            reg = <0>;
+            vddi-supply = <&foo>;
+            reset-gpios = <&foo_gpio 0 GPIO_ACTIVE_LOW>;
+        };
+    };
+
+...