ASoC: intel, keembay-i2s: Add info for device to use DMA

Add descriptions for entries needed for audio device to use DMA
channels for audio playback and capture.
Signed-off-by: Michael Sit Wei Hong <michael.wei.hong.sit@intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20210108031248.20520-5-michael.wei.hong.sit@intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/intel,keembay-i2s.yaml

@@ -45,6 +45,18 @@ properties:
       - const: osc
       - const: apb_clk
 
+  dmas:
+    items:
+      - description: DMA controller phandle and DMA channel
+                     for TX and RX
+
+  dma-names:
+    items:
+      - description: "tx" for the transmit channel
+                     "rx" for the receive channel
+      - const: tx
+      - const: rx
+
 required:
   - compatible
   - "#sound-dai-cells"
@@ -70,4 +82,6 @@ examples:
          interrupts = <GIC_SPI 120 IRQ_TYPE_LEVEL_HIGH>;
          clock-names = "osc", "apb_clk";
          clocks = <&scmi_clk KEEM_BAY_PSS_AUX_I2S3>, <&scmi_clk KEEM_BAY_PSS_I2S3>;
+         dmas = <&axi_dma0 29 &axi_dma0 33>;
+         dma-names = "tx", "rx";
      };