mfd: Add mfd_clone_cell(), convert cs5535-mfd/olpc-xo1 to it

Replace mfd_shared_platform_driver_register with mfd_clone_cell.  The
former was called by an mfd client, and registered both a platform driver
and device.  The latter is called by an mfd driver, and registers only a
platform device.

The downside of this is that mfd drivers need to be modified whenever
new clients are added that share a cell; the upside is that it fits
Linux's driver model better.  It's also simpler.

This also converts cs5535-mfd/olpc-xo1 from the old API.  cs5535-mfd
now creates the olpc-xo1-{acpi,pms} devices, while olpc-xo1 binds to
them via platform drivers.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>