i2c-mpc: Use i2c_add_numbered_adapter

Move the i2c-mpc driver over to using the new i2c infrastructure.
Specifically, it now uses i2c_add_numbered_adapter so that the bus number
can be determined ahead of time and used to register i2c clients before
the bus is instantiated.

Tested on an MPC5200 based board

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Jean Delvare <khali@linux-fr.org>