ASoC: dt-bindings: fsl_spdif: Add compatible string for new platforms

Add compatible string for new added platforms which support spdif module.
They are i.MX8QXP, i.MX8MM, i.MX8MN, i.MX8MQ.
Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Link: https://lore.kernel.org/r/1615884053-4264-1-git-send-email-shengjiu.wang@nxp.comSigned-off-by: Mark Brown <broonie@kernel.org>

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

@@ -21,6 +21,10 @@ properties:
       - fsl,vf610-spdif
       - fsl,imx6sx-spdif
       - fsl,imx8qm-spdif
+      - fsl,imx8qxp-spdif
+      - fsl,imx8mq-spdif
+      - fsl,imx8mm-spdif
+      - fsl,imx8mn-spdif
 
   reg:
     maxItems: 1