BACKPORT: perf: Introduce perf_pmu_migrate_context()

Originally from Peter Zijlstra. The helper migrates perf events
from one cpu to another cpu.

FPIIM-2037

Signed-off-by: Zheng Yan <zheng.z.yan@intel.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1339741902-8449-5-git-send-email-zheng.z.yan@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 70d0e9f12d9b7229b12699fb8f1173a690bd7be3)

Change-Id: I66d7943600ff9c198d690807d07f8c45dc40c662
2 files changed