drm/nouveau/therm: survive to suspend/resume cycles

Therm uses 3 ptimer alarms. Two to drive the fan and one for polling the
temperature. When suspending/resuming, alarms will never be fired.
As we are checking if there isn't an alarm pending before rescheduling
another one, we end up never checking temperature or updating the
fan speed.

This commit also adds debug messages to be able to spot more easily
if this case happens again in the future. Sorry for the spam if you
activate the debug level though.

Tested-by: Dash Four <mr.dash.four@googlemail.com>

v2:
- fix temperature polling too

Signed-off-by: Martin Peres <martin.peres@labri.fr>
Tested-by: Martin Peres <martin.peres@labri.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>