ASoC: bindings: fsl-asoc-card: Add mclk-id optional property

Support setting the sound card main clock input from the device-tree
using the mclk-id property.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>
Link: https://lore.kernel.org/r/20220117132109.283365-4-ariel.dalessandro@collabora.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/fsl-asoc-card.txt

@@ -82,6 +82,7 @@ Optional properties:
   - dai-format		: audio format, for details see simple-card.yaml.
   - frame-inversion	: dai-link uses frame clock inversion, for details see simple-card.yaml.
   - bitclock-inversion	: dai-link uses bit clock inversion, for details see simple-card.yaml.
+  - mclk-id		: main clock id, specific for each card configuration.
 
 Optional unless SSI is selected as a CPU DAI: