dt-bindings: mediatek: mt6359: add codec document

This patch adds MediaTek MT6359 codec document.

Signed-off-by: Jiaxin Yu <jiaxin.yu@mediatek.com>
Link: https://lore.kernel.org/r/1597913493-10747-3-git-send-email-jiaxin.yu@mediatek.com


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