nvme: Greatly improve error recovery

Next phase of error recovery: Eliminate the REOVERY_START phase, since
we don't need to wait to start recovery. Eliminate the RECOVERY_RESET
phase since it is transient, we now transition from RECOVERY_NORMAL into
RECOVERY_WAITING.

In normal mode, read the status of the controller. If it is in failed
state, or appears to be hot-plugged, jump directly to reset which will
sort out the proper things to do. This will cause all pending I/O to
complete with an abort status before the reset.

When in the NORMAL state, call the interrupt handler. This will complete
all pending transactions when interrupts are broken or temporarily
misbehaving. We then check all the pending completions for timeouts. If
we have abort enabled, then we'll send an abort. Otherwise we'll assume
the controller is wedged and needs a reset. By calling the interrupt
handler here, we'll avoid an issue with the current code where we
transitioned to RECOVERY_START which prevented any completions from
happening. Now completions happen. In addition and follow-on I/O that is
scheduled in the completion routines will be submitted, rather than
queued, because the recovery state is correct. This also fixes a problem
where I/O would timeout, but never complete, leading to hung I/O.

Resetting remains the same as before, just when we chose to reset has
changed.

A nice side effect of these changes is that we now do I/O when
interrupts to the card are totally broken. Followon commits will improve
the error reporting and logging when this happens. Performance will be
aweful, but will at least be minimally functional.

There is a small race when we're checking the completions if interrupts
are working, but this is handled in a future commit.

Sponsored by: Netflix
MFC After: 2 weeks
Differential Revision: https://reviews.freebsd.org/D36922