Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r257093:

Be a little more suspicious of thermal sensors, which can have single
crazy readings occasionally. One wild reading should not be enough to
trigger a shutdown, so instead wait for several concerning readings in
a row.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Mark MALLOC_DEFINEs static that have no corresponding MALLOC_DECLAREs.

This means that their use is restricted to a single C file.

- Introduce a define for ZERO_C_TO_K.
- Fix the printing of the temperature when we exceed the critical value.

Approved by: nwhitehorn (mentor)

Use kproc_exit() instead of returning from the management function on
systems with no manageable thermal control devices.

Add some error handling here: if a sensor returns an error code (a negative
Kelvin temperature, which is impossible except for some contrived magnetic
spin systems), use the previous measurement from that sensor instead of
corrupting everything and randomly changing the fans or shutting off the
machine.

Don't put negative values into the averages.

Factor out the SMU fan management code into a new module (powermac_thermal)
that will connect all of the various sensors and fan control modules on
Apple hardware with software-controlled fans (e.g. all G5 systems).

MFC after: 1 month