ASoC: dt-bindings: Introduce compatible string for imx8qm

Register map for i.MX8QM is similar with i.MX6 series. Integration
of SAI IP into i.MX8QM SOC features a FIFO size of 64 X 32 bits samples.
Signed-off-by: NDaniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20190814082911.665-3-daniel.baluta@nxp.comSigned-off-by: NMark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/fsl-sai.txt

@@ -9,7 +9,8 @@ Required properties:
 
   - compatible		: Compatible list, contains "fsl,vf610-sai",
 			  "fsl,imx6sx-sai", "fsl,imx6ul-sai",
-			  "fsl,imx7ulp-sai" or "fsl,imx8mq-sai".
+			  "fsl,imx7ulp-sai", "fsl,imx8mq-sai" or
+			  "fsl,imx8qm-sai".
 
   - reg			: Offset and length of the register set for the device.