perf: Export perf_assign_events()

Export perf_assign_events() so the uncore code can use it to
schedule events.

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/1339741902-8449-2-git-send-email-zheng.z.yan@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>