tools/power turbostat: re-factor sysfs code

Probe cpuidle "sysfs" residency and counts separately,
since soon we will make one disabled on, and the
other disabled off.

Clarify that some BIC (build-in-counters) are actually "groups".
since we're about to re-name some of those groups.

no functional change.

Signed-off-by: Len Brown <len.brown@intel.com>