tools/power turbostat: Clustered Uncore MHz counters should honor show/hide options

The clustered uncore frequency counters, UMHz*.*
should honor the --show and --hide options.

All non-specified counters should be implicityly hidden.
But when --show was used, UMHz*.* showed up anyway:

$ sudo turbostat -q -S --show Busy%
Busy%  UMHz0.0  UMHz1.0  UMHz2.0  UMHz3.0  UMHz4.0

Indeed, there was no string that can be used to explicitly
show or hide clustered uncore counters.

Even through they are dynamically probed and added,
group the clustered UMHz*.* counters with the legacy
built-in-counter "UncMHz" for show/hide.

turbostat --show Busy%
	does not show UMHz*.*.
turbostat --show UncMHz
	shows either UncMHz or UMHz*.*, if present
turbostat --hide UncMHz
	hides either UncMHz or UMHz*.*, if present

Reported-by: Artem Bityutskiy <artem.bityutskiy@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Tested-by: Artem Bityutskiy <artem.bityutskiy@intel.com>