ionic: add FW_STOPPING state

Between fw running and fw actually stopped into reset, we need
a fw_stopping concept to catch and block some actions while
we're transitioning to FW_RESET state.  This will help to be
sure the fw_up task is not scheduled until after the fw_down
task has completed.

On some rare occasion timing, it is possible for the fw_up task
to try to run before the fw_down task, then not get run after
the fw_down task has run, leaving the device in a down state.
This is possible if the watchdog goes off in between finding the
down transition and starting the fw_down task, where the later
watchdog sees the FW is back up and schedules a fw_up task.

Fixes: c672412f ("ionic: remove lifs on fw reset")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>