perf: add hotplug support so that perf continues after hotplug

Current code doesn't restart perf after hotplug and power collapse
which makes monitoring in low power modes difficult. This patch adds
support for the hotplug notifier events and creates a common path for
the power collapse and hotplug events.

Change-Id: I52e6978b1c104fd78bc42e4600ceb111b47b3e11
Signed-off-by: Patrick Fay <pfay@codeaurora.org>