tifm: replace per-adapter kthread with freezeable workqueue

Freezeable workqueue makes sure that adapter work items (device insertions
and removals) would be handled after the system is fully resumed. Previously
this was achieved by explicit freezing of the kthread.

Signed-off-by: Alex Dubov <oakad@yahoo.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>