dt-bindings: add binding for tft displays based on ilitek,ili9486

This binding is for the tft displays based on ilitek,ili9486.
ozzmaker,piscreen and waveshare,rpi-lcd-35 are such displays
Signed-off-by: Kamlesh Gurudasani <kamlesh.gurudasani@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/8938c7a53598db793bbcddf205dcf35bcc19a18e.1581270802.git.kamlesh.gurudasani@gmail.com

Documentation/devicetree/bindings/display/ilitek,ili9486.yaml

+# SPDX-License-Identifier: GPL-2.0-only
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/ilitek,ili9486.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ilitek ILI9486 display panels device tree bindings
+
+maintainers:
+  - Kamlesh Gurudasani <kamlesh.gurudasani@gmail.com>
+
+description:
+  This binding is for display panels using an Ilitek ILI9486 controller in SPI
+  mode.
+
+allOf:
+  - $ref: panel/panel-common.yaml#
+
+properties:
+  compatible:
+    items:
+      - enum:
+          # Waveshare 3.5" 320x480 Color TFT LCD
+        - waveshare,rpi-lcd-35
+          # Ozzmaker 3.5" 320x480 Color TFT LCD
+        - ozzmaker,piscreen
+      - const: ilitek,ili9486
+
+  spi-max-frequency:
+    maximum: 32000000
+
+  dc-gpios:
+    maxItems: 1
+    description: Display data/command selection (D/CX)
+
+  backlight: true
+  reg: true
+  reset-gpios: true
+  rotation: true
+
+required:
+  - compatible
+  - reg
+  - dc-gpios
+  - reset-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    backlight: backlight {
+            compatible = "gpio-backlight";
+            gpios = <&gpio 22 GPIO_ACTIVE_HIGH>;
+    };
+    spi {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+
+            display@0{
+                    compatible = "waveshare,rpi-lcd-35", "ilitek,ili9486";
+                    reg = <0>;
+                    spi-max-frequency = <32000000>;
+                    dc-gpios = <&gpio0 24 GPIO_ACTIVE_HIGH>;
+                    reset-gpios = <&gpio0 25 GPIO_ACTIVE_HIGH>;
+                    rotation = <180>;
+                    backlight = <&backlight>;
+            };
+    };
+
+...