dt-bindings: display: convert ilitek,ili9322 to DT Schema

The .txt binding explains:

"
    The following optional properties only apply to
    RGB and YUV input modes and
    can be omitted for BT.656 input modes:
"

This constraint is not implmented in the DT Schema.

The original binding from the .txt file referenced
properties that is included in panel-timing.yaml.

The properties in question are:
  - pixelclk-active
  - de-active
  - hsync-active
  - vsync-active

These properties was dropped in the conversion as they are not relevant.

v2:
  - drop properties from panel-timing (Linus)
  - drop use of spi-slave.yaml (Maxime)
  - introduce unevaluatedProperties (Maxime)
  - dropped unused properties (Linus)
  - delete stray spaces

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408195109.32692-8-sam@ravnborg.org
diff --git a/Documentation/devicetree/bindings/display/panel/ilitek,ili9322.yaml b/Documentation/devicetree/bindings/display/panel/ilitek,ili9322.yaml
new file mode 100644
index 0000000..177d48c
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/panel/ilitek,ili9322.yaml
@@ -0,0 +1,71 @@
+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/panel/ilitek,ili9322.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ilitek ILI9322 TFT panel driver with SPI control bus
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+description: |
+  This is a driver for 320x240 TFT panels, accepting a variety of input
+  streams that get adapted and scaled to the panel. The panel output has
+  960 TFT source driver pins and 240 TFT gate driver pins, VCOM, VCOML and
+  VCOMH outputs.
+
+  The panel must obey the rules for a SPI slave device as specified in
+  spi/spi-controller.yaml
+
+allOf:
+  - $ref: panel-common.yaml#
+
+properties:
+  compatible:
+    items:
+      - enum:
+        - dlink,dir-685-panel
+
+      - const: ilitek,ili9322
+
+  reset-gpios: true
+  port: true
+
+  vcc-supply:
+    description: Core voltage supply
+
+  iovcc-supply:
+    description: Voltage supply for the interface input/output signals
+
+  vci-supply:
+    description: Voltage supply for analog parts
+
+required:
+  - compatible
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    spi {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        panel: display@0 {
+            compatible = "dlink,dir-685-panel", "ilitek,ili9322";
+            reg = <0>;
+            vcc-supply = <&vdisp>;
+            iovcc-supply = <&vdisp>;
+            vci-supply = <&vdisp>;
+
+            port {
+                panel_in: endpoint {
+                    remote-endpoint = <&display_out>;
+                };
+            };
+        };
+    };
+
+...