Perf: keep events across hotplug
Keep event list alive across a CPU hotplug so that perf can resume when the CPU comes back online. Bring a CPU online when exiting a perf session so it can be cleaned up properly. Change-Id: Ie0e4a43f751beb77afdc84e9d52b21780f279d80 Signed-off-by: Neil Leeder <nleeder@codeaurora.org>

Signed-off-by: evolutionmod <kernelcraft@gmail.com>