tools/power turbostat: Add MTL's PMT DC6 builtin counter

Provide a definition for metadata that allows reading DC6 residency
counter via PMT and exposes it as a builtin counter.

Note that this residency counter is updated and read via
entirely different mechanisms vs the MSR-based residency counters.
On MTL processors, there are times when Die%c6 will report above 100%.
This is still useful, but don't expect 3 digits of precision...

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