ASoC: dt-bindings: mediatek: mt6358: add dmic-mode property

Adds dmic-mode property and updates example.

Signed-off-by: Jiaxin Yu <jiaxin.yu@mediatek.com>
Link: https://lore.kernel.org/r/1591353222-18576-3-git-send-email-jiaxin.yu@mediatek.com


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