ASoC: dt-bindings: imx-hdmi: Add binding doc for hdmi machine driver

Imx-hdmi is a new added machine driver for supporting hdmi devices
on i.MX platforms. There is HDMI IP or external HDMI modules connect
with SAI or AUD2HTX interface.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1607251319-5821-1-git-send-email-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/imx-audio-hdmi.yaml

@@ -0,0 +1,52 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/imx-audio-hdmi.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: NXP i.MX audio complex with HDMI
+
+maintainers:
+  - Shengjiu Wang <shengjiu.wang@nxp.com>
+
+properties:
+  compatible:
+    enum:
+      - fsl,imx-audio-hdmi
+      - fsl,imx-audio-sii902x
+
+  model:
+    $ref: /schemas/types.yaml#/definitions/string
+    description: User specified audio sound card name
+
+  audio-cpu:
+    description: The phandle of an CPU DAI controller
+
+  hdmi-out:
+    description: |
+      This is a boolean property. If present, the transmitting function
+      of HDMI will be enabled, indicating there's a physical HDMI out
+      connector or jack on the board or it's connecting to some other IP
+      block, such as an HDMI encoder or display-controller.
+
+  hdmi-in:
+    description: |
+      This is a boolean property. If present, the receiving function of
+      HDMI will be enabled, indicating there is a physical HDMI in
+      connector/jack on the board.
+
+required:
+  - compatible
+  - model
+  - audio-cpu
+
+additionalProperties: false
+
+examples:
+  - |
+    sound-hdmi {
+        compatible = "fsl,imx-audio-hdmi";
+        model = "audio-hdmi";
+        audio-cpu = <&aud2htx>;
+        hdmi-out;
+    };