tools/power turbostat: simplify output, add Avg_MHz

Use 8 columns for each number ouput.
We don't fit into 80 columns on most machines,
so keep the format simple.

Print frequency in MHz instead of GHz.
We've got 8 columns now, so use them to
show low frequency in a more natural unit.

Many users didn't understand what %c0 meant,
so re-name it to be %Busy.

Add Avg_MHz column, which is the frequency that many
users expect to see -- the total number of cycles executed
over the measurement interval.

People found the previous GHz to be confusing, since
it was the speed only over the non-idle interval.
That measurement has been re-named Bzy_MHz.

Suggested-by: Dirk J. Brandewie
Signed-off-by: Len Brown <len.brown@intel.com>