ASoC: dt-bindings: ep93xx: Document DMA support

Document DMA support in binding document.

Signed-off-by: Nikita Shubin <[e-mail]>
Tested-by: Alexander Sverdlin <[e-mail]>
Reviewed-by: Krzysztof Kozlowski <[e-mail]>
Reviewed-by: Mark Brown <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Guenter Roeck <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Acked-by: Miquel Raynal <[e-mail]>
Acked-by: Vinod Koul <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>

Documentation/devicetree/bindings/sound/cirrus,ep9301-i2s.yaml

···
       - const: sclk
       - const: lrclk
 
+  dmas:
+    items:
+      - description: out DMA channel
+      - description: in DMA channel
+
+  dma-names:
+    items:
+      - const: tx
+      - const: rx
+
 required:
   - compatible
   - '#sound-dai-cells'
···
                  <&syscon 30>,
                  <&syscon 31>;
         clock-names = "mclk", "sclk", "lrclk";
+        dmas = <&dma0 0 1>, <&dma0 0 2>;
+        dma-names = "tx", "rx";
     };
 
 ...