ASoC: dt-bindings: qcom: sm8250: Document "aux-devs"

The sm8250 audio driver uses the common Qualcomm device tree parser and
therefore already supports the "aux-devs" property that allows adding
additional auxiliary devices to the sound card (e.g. analog speaker
amplifiers that can be connected using "audio-routing").

Document the property in the DT schema for sm8250 as well. The description
is taken from simple-card.yaml which has a very similar property.

Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211202145505.58852-3-stephan@gerhold.netSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/qcom,sm8250.yaml

@@ -27,6 +27,12 @@ properties:
       being the connection's source. Valid names could be power supplies,
       MicBias of codec and the jacks on the board.
 
+  aux-devs:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    description: |
+      List of phandles pointing to auxiliary devices, such
+      as amplifiers, to be added to the sound card.
+
   model:
     $ref: /schemas/types.yaml#/definitions/string
     description: User visible long sound card name