dt-bindings: iio: adc: add bindings doc for MT6360 ADC

This change adds the binding doc for the MT6360 ADC.
Signed-off-by: Gene Chen <gene_chen@richtek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1603181267-15610-2-git-send-email-gene.chen.richtek@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/mediatek,mt6360-adc.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/mediatek,mt6360-adc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Mediatek MT6360 and similar ADCs
+
+maintainers:
+  - Gene Chen <gene_chen@richtek.com>
+
+properties:
+  compatible:
+    const: mediatek,mt6360-adc
+
+  "#io-channel-cells":
+    const: 1
+
+required:
+  - compatible
+  - "#io-channel-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    adc {
+      compatible = "mediatek,mt6360-adc";
+      #io-channel-cells = <1>;
+    };
+...