Automatically discover MSRs

[connorimes]

If the ENERGYMON_MSRS env var is not set, energymon-msr should attempt to discover which MSRs to use. We currently just default to cpu0. Can't just use all MSRs because multiple cores will expose the same MSR.

• Can we guarantee that a single MSR per processor socket is all that's needed? If so, that makes the task a little easier.
• Potential options using the shell:
  • lscpu
  • numactl -H (requires numactl to be installed)
• Can we discover processor architecture through C/POSIX functions?

[connorimes]

Closing as wontfix. The raplcap-msr implementation introduced in v0.3.0 (over 2 years ago) provides automatic package/die detection and better Intel CPU support. Commit bb59d58 now documents this in the msr README file.