ASoC: mediatek: mt8186: add mt8186-mt6366-da7219-max98357 document

Add document for mt8186 board with mt6366, da7219 and max98357.

Signed-off-by: Jiaxin Yu <jiaxin.yu@mediatek.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220718162204.26238-7-jiaxin.yu@mediatek.com


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