dt-bindings: i2c: Add Mediatek MT2701 i2c binding

Add MT2701 i2c binding to i2c-mt6577.txt and there is no need to
modify i2c driver.

Signed-off-by: Jun Gao <jun.gao@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>