Some G5s still occasionally experience shutdowns due to overtemp
conditions despite the recent fix. After analyzing logs from such
machines, it appears that the overtemp code is a bit too quick at
shutting the machine down when reaching the critical temperature (tmax +
8) and doesn't leave the fan enough time to actually cool it down. This
happens if the temperature of a CPU suddenly rises too high in a very
short period of time, or occasionally on boot (that is the CPUs are
already overtemp by the time the driver loads).

This patches makes the code a bit more relaxed, leaving a few seconds to
the fans to do their job before kicking the machine shutown.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>