ASoC: dt-bindings: simple-mux: add idle-state property

simple-mux immediately activates the new output, even when it is powered
down. This can be undesirable in some cases, for example when a
mechanical relais is used.
Adds "idle-state" property from the mux controller to select the output
state to be used when the mux is powered down.

Signed-off-by: Hendrik v. Raven <h.v.raven@merzmedtech.de>
Link: https://patch.msgid.link/20241114-simple-mux-idle-state-v2-2-a30cb37d2be2@merzmedtech.de
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Hendrik v. Raven

Documentation/devicetree/bindings/sound/simple-audio-mux.yaml

@@ -29,6 +29,10 @@ properties:
     $ref: /schemas/types.yaml#/definitions/string-array
     maxItems: 2
 
+  idle-state:
+    description: If present specifies the state when the mux is powered down
+    $ref: /schemas/mux/mux-controller.yaml#/properties/idle-state
+
   sound-name-prefix: true
 
 required:
@@ -43,4 +47,5 @@ examples:
         compatible = "simple-audio-mux";
         mux-gpios = <&gpio 3 0>;
         state-labels = "Label_A", "Label_B";
+        idle-state = <0>;
     };