ichwd: Don't disable watchdog when rebooting

[jhibbits]

Summary

The ichwd driver shares ichwd_detach for both detach and shutdown, since
some operations are necessary in both cases. However, this causes the
watchdog to be disabled for shutdown/reboot, so any problems during the
reboot process could hang until manual intervention. To fix this, keep
the shared handler, but only disable the watchdog when not rebooting.

Sponsored by: Hewlett-Packard Enterprise

[kib]

I think users must have ability to get back to the previous behavior. Might be add a sysctl to tweak it.

[jhibbits]

rebooting != rebooting, but rather 'going through shutdown path'.