tools/power turbostat: Allow adding PMT counters directly by sysfs path

Allow user to add PMT counters by either identifying the source with:
  guid=%u,seq=%u
or, since this patch, with direct sysfs path:
  path=%s, for example path=/sys/class/intel_pmt/telem5

In the later case, the guid and sequence number will be infered
by turbostat.

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