ASoC: dt-bindings: fsl,sai: Add AUDMIX mode support on i.MX952

The SAI can connect to AUDMIX, but AUDMIX can be bypassed or not on
i.MX952. There are three use cases:

1) SAI -> Codec (No AUDMIX between SAI and Codec)
2) SAI -> Codec (Has AUDMIX, but AUDMIX is bypassed)
3) SAI -> AUDMIX -> Codec (Has AUDMIX and used)

So add 'fsl,sai-amix-mode' property for this feature

fsl,sai-amix-mode = "none": is for case 1)
fsl,sai-amix-mode = "bypass": is for case 2)
fsl,sai-amix-mode = "audmix": is for case 3)

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://patch.msgid.link/20260123082501.4050296-3-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/fsl,sai.yaml

@@ -132,6 +132,13 @@ properties:
         - description: dataline mask for 'rx'
         - description: dataline mask for 'tx'
 
+  fsl,sai-amix-mode:
+    $ref: /schemas/types.yaml#/definitions/string
+    description:
+      The audmix module is bypassed from hardware or not.
+    enum: [none, bypass, audmix]
+    default: none
+
   fsl,sai-mclk-direction-output:
     description: SAI will output the SAI MCLK clock.
     type: boolean
@@ -179,6 +186,15 @@ allOf:
       properties:
         fsl,sai-synchronous-rx: false
 
+  - if:
+      required:
+        - fsl,sai-amix-mode
+    then:
+      properties:
+        compatible:
+          contains:
+            const: fsl,imx952-sai
+
 required:
   - compatible
   - reg