dt-bindings: input: touchscreen: Add Hynitron cstxxx

Add documentation for the Hynitron cstxxx touchscreen bindings.
Hynitron makes a series of touchscreen controllers, however for
now this is expected to only be compatible with the cst3xx series,
specifically the CST340, CST348, and CST356.
Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221028202636.14341-3-macroalpha82@gmail.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/hynitron,cstxxx.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/input/touchscreen/hynitron,cstxxx.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Hynitron cstxxx series touchscreen controller
+
+description: |
+  Bindings for Hynitron cstxxx series multi-touch touchscreen
+  controllers.
+
+maintainers:
+  - Chris Morgan <macromorgan@hotmail.com>
+
+allOf:
+  - $ref: touchscreen.yaml#
+
+properties:
+  compatible:
+    enum:
+      - hynitron,cst340
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  reset-gpios:
+    maxItems: 1
+
+  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/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    i2c {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      touchscreen@1a {
+        compatible = "hynitron,cst340";
+        reg = <0x1a>;
+        interrupt-parent = <&gpio4>;
+        interrupts = <9 IRQ_TYPE_EDGE_FALLING>;
+        reset-gpios = <&gpio4 6 GPIO_ACTIVE_LOW>;
+        touchscreen-size-x = <640>;
+        touchscreen-size-y = <480>;
+      };
+    };
+
+...