This I2C driver framework has some major differences compared to libi2c.
* It is compatible to the Linux I2C user-space API.
* It uses generic IMFS nodes and thus reduces the levels of indirection.
* The drivers don't have to mess around with minor numbers to get their
state information.
* No arbitrary bus controller model is assumed. The main task of an I2C
bus controller driver is to process I2C messages. How this is done is
private to the driver.
* Scatter/gather operations are supported (I2C_M_NOSTART).
