tools/power turbostat: read RAPL counters via perf

Some of the future Intel platforms will require reading the RAPL
counters via perf and not MSR. On current platforms we can still read
them using both ways.

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