dt-bindings: input/touchscreen: add bindings for msg2638

This adds dts bindings for the mstar msg2638 touchscreen.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210305153815.126937-1-vincent.knecht@mailoo.orgSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/mstar,msg2638.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/input/touchscreen/mstar,msg2638.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MStar msg2638 touchscreen controller Bindings
+
+maintainers:
+  - Vincent Knecht <vincent.knecht@mailoo.org>
+
+allOf:
+  - $ref: touchscreen.yaml#
+
+properties:
+  compatible:
+    const: mstar,msg2638
+
+  reg:
+    const: 0x26
+
+  interrupts:
+    maxItems: 1
+
+  reset-gpios:
+    maxItems: 1
+
+  vdd-supply:
+    description: Power supply regulator for the chip
+
+  vddio-supply:
+    description: Power supply regulator for the I2C bus
+
+  touchscreen-size-x: true
+  touchscreen-size-y: true
+
+additionalProperties: false
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - reset-gpios
+  - touchscreen-size-x
+  - touchscreen-size-y
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      touchscreen@26 {
+        compatible = "mstar,msg2638";
+        reg = <0x26>;
+        interrupt-parent = <&msmgpio>;
+        interrupts = <13 IRQ_TYPE_EDGE_FALLING>;
+        reset-gpios = <&msmgpio 100 GPIO_ACTIVE_LOW>;
+        pinctrl-names = "default";
+        pinctrl-0 = <&ts_int_reset_default>;
+        vdd-supply = <&pm8916_l17>;
+        vddio-supply = <&pm8916_l5>;
+        touchscreen-size-x = <2048>;
+        touchscreen-size-y = <2048>;
+      };
+    };
+
+...