kernel - Fix boot-time panic in NATA revealed by new callout mechanics

kernel - Fix boot-time panic in NATA revealed by new callout mechanics

* The NATA driver was using spin locks in a very, very dangerous way.
  They did not play nice with the new blocking callout mechanism.

* Replace all of NATAs spinlocks with lockmgr locks.  In addition, change
  all asynchronous callout_stop() calls to synchronous callout_stop_sync()
  calls, and use callout_init_lk() to auto-lock ch->state_lock for the
  callback, which fixes a long-time deadlock race.

Reported-by: tuxillo