New port: sysutils/intel-undervolt

intel-undervolt is a tool for undervolting Haswell and newer Intel
CPUs using MSR. Also allows to alter power limits and temperature
limit using MSR and MCHBAR registers.

Use at your own risk.

WWW: https://github.com/kitsunyan/intel-undervolt

Submitted by: greg@unrelenting.technology
Reviewed by: arrowd, 0mp, tobik
Differential Revision: https://reviews.freebsd.org/D18729