Merge branch 'idle-time-acc' into features

Merge branch 'idle-time-acc' into features

Heiko Carstens says:

===================
This is supposed to improve s390 idle time accounting, and brings it
back to the state it was before arch_cpu_idle_time() was removed from
s390 [3].

In result all cpu time accounting is done by the s390 architecture backend
again, instead of having a mix of architecure specific and common code
accounting (common code: idle, s390 architecture: everything else).
===================

Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>