ASoC: audio-graph-card: Add clocks property to endpoint node

Add optional 'clocks' property to audio port 'endpoint' node. One
such example is where SoC supplies a clock to external audio codec
component.

Signed-off-by: Sameer Pujar <spujar@nvidia.com>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Link: https://lore.kernel.org/r/1611944866-29373-4-git-send-email-spujar@nvidia.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/audio-graph-port.yaml

@@ -33,6 +33,9 @@ properties:
         properties:
           remote-endpoint:
             maxItems: 1
+          clocks:
+            maxItems: 1
+            description: Describes the clock used by audio component.
           mclk-fs:
             description: |
               Multiplication factor between stream rate and codec mclk.