ASoC: dt-bindings: mediatek,mt8188-afe: add audio afe document

Add mt8188 audio afe document.

Signed-off-by: Trevor Wu <trevor.wu@mediatek.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230116034131.23943-11-trevor.wu@mediatek.com


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