dt-bindings: mediatek: Adds a DT binding documentation for the MT6582 SoC

This adds a DT binding documentation for the MT6582 SoC.

Signed-off-by: Maxim Kutnij <gtk3@inbox.ru>
Link: https://lore.kernel.org/r/20211219183134.3849-3-gtk3@inbox.ru


[mb: fix commit subject line and compatible order]
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>