coretemp: Only log critical temperature events

According to the Intel manual
https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-vol-3b-part-2-manual.pdf
the Thermal Status (0) and Thermal Status Log (1) bits report only a
high temperature on the CPU, not a critical temperature as suggested in
the coretemp driver. Check the Critical Temperature Log (5) instead.
The critical temperature waives guarantees of correct function,
therefore the CPU could have for example written some wrong values into
memory at that point and the OS should be stopped ASAP as the state is
no longer reliable.

Reviewed by: imp (confirmed descriptions of bits, linux ignores these bits)
Pull Request: https://github.com/freebsd/freebsd-src/pull/562