MFC r340426 (by cem)

amdtemp(4): Fix temperature reporting on AMD 2990WX

Update the AMD family 17h temperature reporting based on AMD Tech Doc 56255
OSRR, section 4.2.1.

For CPUS w/CUR_TEMP_RANGE_SEL set, scale the reported temperature into the
range -49..206; i.e., subtract 49°C.

Submitted by: gallatin@
Reported by: bcran@
Reviewed by: cem (long ago)
Approved by: re (kib)
Relnotes: yes
Differential Revision: https://reviews.freebsd.org/D16855