ASoC: dt-bindings: imx-audio-spdif: convert to YAML

Convert the imx-audio-spdif binding to YAML.

When testing dtbs_check, found below compatible strings
are not listed in document:

fsl,imx-sabreauto-spdif
fsl,imx6sx-sdb-spdif

So add them in yaml file to pass the test.

Signed-off-by: Shengjiu Wang <shengjiu.wang@nxp.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://msgid.link/r/1712830305-31350-2-git-send-email-shengjiu.wang@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>