tools/power turbostat: Allow printing header every N iterations

This gives the ability to reprint the header every N iterations, so you
can ensure that a scrolling display always has the header visible
somewhere on the screen.

Signed-off-by: Zephaniah E. Loss-Cutler-Hull <zephaniah@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>