i2c-designware: move controller config to bus specific portion of driver

With multiple I2C adapters possible in the system each running at
(possibly) different speeds we need to move the controller
configuration bit field to the adapter.

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>