[RFE] add hinv metric to describe CPU hyperthreading

Its been requested that the machines CPU hyperthreading state be exposed through additional hinv metrics from pmdalinux.

This information is available by looking in /sys/devices/system/cpu/cpu0/topology/thread_siblings_list (multiple values here indicate hyperthreading is active, e.g. 0,1,2,3) and also the sibling value in /proc/cpuinfo (which is a more architecture dependent method).