Revert "ARM: disable preemption in machine_shutdown"

This reverts commit c69652ca4c9420d96275a6772c9f03255b582f4a.
ondemand: backport from kernel 3.2

Change-Id: I677f17a0a29be57df0e51d88e884f3c641443cf5
Staging: logger: backport 3.8 logger