dt-bindings: input: touchscreen: ilitek_ts_i2c: Add bindings

Add binding documentation for ILITEK touch devices.
Signed-off-by: Joe Hung <joe_hung@ilitek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210324122601.125873-1-joe_hung@ilitek.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/ilitek_ts_i2c.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/input/touchscreen/ilitek_ts_i2c.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Ilitek I2C Touchscreen Controller
+
+maintainers:
+  - Dmitry Torokhov <dmitry.torokhov@gmail.com>
+
+allOf:
+  - $ref: touchscreen.yaml#
+
+properties:
+  compatible:
+    enum:
+      - ilitek,ili2130
+      - ilitek,ili2131
+      - ilitek,ili2132
+      - ilitek,ili2316
+      - ilitek,ili2322
+      - ilitek,ili2323
+      - ilitek,ili2326
+      - ilitek,ili2520
+      - ilitek,ili2521
+
+  reg:
+    const: 0x41
+
+  interrupts:
+    maxItems: 1
+
+  reset-gpios:
+    maxItems: 1
+
+  wakeup-source:
+    type: boolean
+    description: touchscreen can be used as a wakeup source.
+
+  touchscreen-size-x: true
+  touchscreen-size-y: true
+  touchscreen-inverted-x: true
+  touchscreen-inverted-y: true
+  touchscreen-swapped-x-y: true
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - reset-gpios
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/gpio/gpio.h>
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        touchscreen@41 {
+            compatible = "ilitek,ili2520";
+            reg = <0x41>;
+
+            interrupt-parent = <&gpio1>;
+            interrupts = <7 IRQ_TYPE_LEVEL_LOW>;
+            reset-gpios = <&gpio1 8 GPIO_ACTIVE_LOW>;
+            touchscreen-inverted-y;
+            wakeup-source;
+        };
+    };