cpupower: Make monitor command -c/--cpu aware

This allows for example:
cpupower -c 2-4,6 monitor -m Mperf
              |Mperf
PKG |CORE|CPU | C0   | Cx   | Freq
   0|   8|   4|  2.42| 97.58|  1353
   0|  16|   2| 14.38| 85.62|  1928
   0|  24|   6|  1.76| 98.24|  1442
   1|  16|   3| 15.53| 84.47|  1650

CPUs always get resorted for package, core then cpu id if it could get read out
(or however you name these topology levels...).
Still this is a nice way to keep the overview if a test binary is bound to
a specific CPU or if one wants to show all CPUs inside a package or similar.

Still missing: Do not measure not available cores to reduce the overhead
and achieve better results.

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>