[GIT PULL] cputime: More cleanups v2

Hi Ingo, Thomas, Seconds take for these cleanups (and more are to come). I haven't got reviews in two weeks so I'm resending with a pull request. Changes in v2: * Fix wrong condition when using is_idle_task() (patch 2/6) * Remove unnecessary !S390 dependency for finegrained irqtime accounting

[GIT PULL] cputime: More cleanups v2

Hi Ingo, Thomas, Seconds take for these cleanups (and more are to come). I haven't got reviews in two weeks so I'm resending with a pull request. Changes in v2: * Fix wrong condition when using is_idle_task() (patch 2/6) * Remove unnecessary !S390 dependency for finegrained irqtime accounting