ASoC: dt-bindings: Add audio-iio-aux

Industrial I/O devices can be present in the audio path.
These devices needs to be viewed as audio components in order to be
fully integrated in the audio path.

audio-iio-aux allows to consider these Industrial I/O devices as
auxliary audio devices.

Signed-off-by: Herve Codina <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Reviewed-by: Christophe Leroy <christophe.leroy@©sgroup.eu>
Reviewed-by: Christophe Leroy <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/audio-iio-aux.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/audio-iio-aux.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Audio IIO auxiliary
+
+maintainers:
+  - Herve Codina <[e-mail]>
+
+description:
+  Auxiliary device based on Industrial I/O device channels
+
+allOf:
+  - $ref: dai-common.yaml#
+
+properties:
+  compatible:
+    const: audio-iio-aux
+
+  io-channels:
+    description:
+      Industrial I/O device channels used
+
+  io-channel-names:
+    description:
+      Industrial I/O channel names related to io-channels.
+      These names are used to provides sound controls, widgets and routes names.
+
+  snd-control-invert-range:
+    $ref: /schemas/types.yaml#/definitions/uint32-array
+    description: |
+      A list of 0/1 flags defining whether or not the related channel is
+      inverted
+    items:
+      enum: [0, 1]
+      default: 0
+      description: |
+        Invert the sound control value compared to the IIO channel raw value.
+          - 1: The related sound control value is inverted meaning that the
+               minimum sound control value correspond to the maximum IIO channel
+               raw value and the maximum sound control value correspond to the
+               minimum IIO channel raw value.
+          - 0: The related sound control value is not inverted meaning that the
+               minimum (resp maximum) sound control value correspond to the
+               minimum (resp maximum) IIO channel raw value.
+
+required:
+  - compatible
+  - io-channels
+  - io-channel-names
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    iio-aux {
+        compatible = "audio-iio-aux";
+        io-channels = <&iio 0>, <&iio 1>, <&iio 2>, <&iio 3>;
+        io-channel-names = "CH0", "CH1", "CH2", "CH3";
+        /* Invert CH1 and CH2 */
+        snd-control-invert-range = <0 1 1 0>;
+    };