Add TWI driver for the PMC-Sierra MSP71xx devices.

[JD: Drop the probe hack, don't set algo_data as we never use it, return
the right error code if the driver registration fails.]
Signed-off-by: Marc St-Jean <Marc_St-Jean@pmc-sierra.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>