perf: don't zombie certain events in perf_event_release_kernel

Ignore events with no particular cpu associated, while
moving the events to zombie state, during event
release.

Change-Id: I11624f3734633ee6c55454be0cd32f638ed61024
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
[rananta@codeaurora.org: resolve trivial merge conflicts]
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>