dt-bindings: iio: adc: convert sd modulator to json-schema

Convert the sigma delta modulator bindings
to DT schema format using json-schema.
Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/sigma-delta-modulator.txt

-Device-Tree bindings for sigma delta modulator
-
-Required properties:
-- compatible: should be "ads1201", "sd-modulator". "sd-modulator" can be use
-	as a generic SD modulator if modulator not specified in compatible list.
-- #io-channel-cells = <0>: See the IIO bindings section "IIO consumers".
-
-Example node:
-
-	ads1202: adc {
-		compatible = "sd-modulator";
-		#io-channel-cells = <0>;
-	};

Documentation/devicetree/bindings/iio/adc/sigma-delta-modulator.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/sigma-delta-modulator.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Device-Tree bindings for sigma delta modulator
+
+maintainers:
+  - Arnaud Pouliquen <arnaud.pouliquen@st.com>
+
+properties:
+  compatible:
+    description: |
+      "sd-modulator" can be used as a generic SD modulator,
+      if the modulator is not specified in the compatible list.
+    enum:
+      - sd-modulator
+      - ads1201
+
+  '#io-channel-cells':
+    const: 0
+
+required:
+  - compatible
+  - '#io-channel-cells'
+
+additionalProperties: false
+
+examples:
+  - |
+    ads1202: adc {
+      compatible = "sd-modulator";
+      #io-channel-cells = <0>;
+    };
+
+...