mpt2sas: use single watchdog workqueue

Collapse the existing per-adapter workqueues, ioc->fault_reset_work,
into a single driver workqueue, mpt2sas_fault_reset_work_q. Since
mpt2sas_fault_reset_work_q exists for the lifetime of the driver, this
simplifies adapter removal and the canceling of its corresponding
watchdog.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>