tools/power turbostat: Allow using cpu device in perf counters on hybrid platforms

Intel hybrid platforms expose different perf devices for P and E cores.
Instead of one, "/sys/bus/event_source/devices/cpu" device, there are
"/sys/bus/event_source/devices/{cpu_core,cpu_atom}".

This, however makes it more complicated for the user,
because most of the counters are available on both and had to be
handled manually.

This patch allows users to use "virtual" cpu device that is seemingly
translated to cpu_core and cpu_atom perf devices, depending on the type
of a CPU we are opening the counter for.

Signed-off-by: Patryk Wlazlyn <patryk.wlazlyn@linux.intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>