dt-bindings: mediatek: add MT6765 power dt-bindings

This adds power dt-bindings for MT6765

Signed-off-by: Mars Cheng <mars.cheng@mediatek.com>
Signed-off-by: Owen Chen <owen.chen@mediatek.com>
Signed-off-by: Macpaul Lin <macpaul.lin@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>