Initial bits of vfs0050 driver.
Enough to get fprint_demo working.

Barely.  This is no image cleanup, no detecting edge of scan, no nothing.

Missing lots of error checking.  Highly experimental at this stage.
Mark activate ssm completed, once deactivate called.

This is kind of counter-intuitive.  Fuck.
Activate ssm should be renamed, it's really the loop
in which we'll keep reading fingerprints until we're
deactivated.
Did I really commit a vim backup?
Fixing up, keeping device in consistent state.

There's nothing obvious anymore that puts the device
in an inconsistent state.  Playing around with fprint_demo,
I can no longer muck it up.  Can start enrollment, cancel,
verify, cancel, etc.  Activate and deactivate are working
properly.