tools/power turbostat: Add RAPL psys as a built-in counter

Introduce the counter as a part of global, platform counters structure.
We open the counter for only one cpu, but otherwise treat it as an
ordinary RAPL counter, allowing for grouped perf read.

The counter is disabled by default, because it's interpretation may
require additional, platform specific information, making it unsuitable
for general use.

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