i2c: muxes: rename first set of drivers to a standard pattern

Apply a naming pattern like in the rest of the subsystem to a first set
of mux drivers. Those drivers are the low-hanging fruit; we want to pick
them to motivate upcoming drivers to follow the new pattern. The missing
GPIO driver will be converted in a later patch.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com> (pca9541)
Acked-by: Jean Delvare <khali@linux-fr.org>