This is a user-facing change to the cc3200's API, to make it conform to the
new machine hardware API. The changes are:
- change I2C constructor to: I2C(id=0, *, freq=100000, scl=None, sda=None)
- change I2C init to: init(*, freq, scl, sda)
- removal of machine.I2C.MASTER constant
- I2C str/repr no longer prints I2C.MASTER
To update existing code it should be enough to just remove the I2C.MASTER
constant from contructor/init for I2C.