tools/power/turbostat: Introduce probe_pm_features()

Feature probe has nothing to do with CPUID, thus it should not be in
process_cpuids().

Introduce probe_pm_features() and move all feature probing functions
into it.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>