perf: Avoid cpu hotplug during event deletion

The event will not be successfully deleted if there was a CPU
hotplug going on. The change prevents that from happening.
Moreover, the change also disables the ARM PMU irq when the CPU
is coming down. This is due to the reason that the deletion
of perf event depends on freeing the irqs, which would happen
if the irq is disabled in the first place.

Change-Id: Ifc3860f723f76d1560e2c9d3fd507e5ead20462a
Signed-off-by: Raghavendra Rao Ananta <rananta@codeaurora.org>