ASoC: dt-bindings: tegra20-i2s: Document new nvidia,fixed-parent-rate property

Document new nvidia,fixed-parent-rate property which instructs that this
board wants parent clock to stay at a fixed rate. It allows to prevent
conflicts between audio components that share same parent PLL. For
instance, this property allows to have HDMI audio, speaker and headphones
in the system playing audio simultaneously, which is a common pattern for
consumer devices.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20211204143725.31646-4-digetx@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/nvidia,tegra20-i2s.yaml

@@ -42,6 +42,13 @@ properties:
       - const: rx
       - const: tx
 
+  nvidia,fixed-parent-rate:
+    description: |
+      Specifies whether board prefers parent clock to stay at a fixed rate.
+      This allows multiple Tegra20 audio components work simultaneously by
+      limiting number of supportable audio rates.
+    type: boolean
+
 required:
   - compatible
   - reg