Fix check that CPU is a valid CPU
Review Request #128085 - Created June 3, 2016 and submitted
We have a check that an devices/system/cpu/cpuN entry contains a processor and not just an empty socket, however it relies on somewhat outdated /sys files. cpuN/cpufreq isn't guaranteed to exist as for some systems (my AMD processor at least). The docs in the linux kernel imply topology/core_id should always exist, and should still work as a valid check that we have a populated CPU socket.