ASoC: bindings: fsl_spdif: Add new compatible string for imx6sx

Add new compatible string "fsl,imx6sx-spdif" in the binding document.
And add compatible string "fsl,vf610-spdif" which was missed before.
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/feda3bb02296455d43aeebb7575918d9b28e1a3f.1592376770.git.shengjiu.wang@nxp.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/fsl,spdif.txt

@@ -6,7 +6,11 @@ a fibre cable.
 
 Required properties:
 
-  - compatible		: Compatible list, must contain "fsl,imx35-spdif".
+  - compatible		: Compatible list, should contain one of the following
+			  compatibles:
+			  "fsl,imx35-spdif",
+			  "fsl,vf610-spdif",
+			  "fsl,imx6sx-spdif",
 
   - reg			: Offset and length of the register set for the device.