ASoC: dt-bindings: meson: convert axg spdif output to schema

Convert the DT binding documentation for the Amlogic axg spdif output to
schema.

Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230206153449.596326-7-jbrunet@baylibre.com


Signed-off-by: Mark Brown <broonie@kernel.org>