ASoC: dt-bindings: add regulator property to simple amplifier

Amplifier may have associated regulator, so add a property for it.
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/simple-amplifier.txt

@@ -4,9 +4,14 @@ Required properties:
 - compatible : "dioo,dio2125" or "simple-audio-amplifier"
 - enable-gpios : the gpio connected to the enable pin of the simple amplifier
 
+Optional properties:
+- VCC-supply   : power supply for the device, as covered
+                 in Documentation/devicetree/bindings/regulator/regulator.txt
+
 Example:
 
 amp: analog-amplifier {
 	compatible = "simple-audio-amplifier";
+	VCC-supply = <&regulator>;
 	enable-gpios = <&gpio GPIOH_3 0>;
 };