tools/power turbostat: Show uncore frequency

When CONFIG_INTEL_UNCORE_FREQ_CONTROL is effective,
(Linux 5.9 and later), print the current (and default)
min and max uncore frequency limits.

When that driver provides the current uncore frequency
(Linux 5.18 and later), print a UncMHz column
reflecting the current uncore frequency.

Note that UncMHz is an instantaneous sample, not an average.

eg.

$ sudo ./turbostat -S --show frequency
...
Uncore Frequency pkg0 die0: 800 - 3900 MHz (800 - 3900 MHz)
...
Avg_MHz	Busy%	Bzy_MHz	TSC_MHz	UncMHz
28	0.70	4049	3095	3900

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