nohz_full left a periodic tick cpu issue

Hi Frederic,

Sorry for idiot of nohz_full. When we using this feature on my mobile devices, we found this feature keep cpu0 in periodic tick mode. then the timer interrupt on cpu0 is very higher than normal nohz mode. that cause high power consuming cost.

I found you have mention this on commit: a382bf934449 nohz: Assign timekeeping duty to a CPU outside the full dynticks range

In fact, if all full dynticks cpu are in idle, cpu0 should be safe to get into idle too. Do you have some plan or idea to implement this? otherwise, power cost is too high to enable nohz_full in mobile platform.