cpuidle: coupled: fix sleeping while atomic in cpu notifier

The cpu hotplug notifier gets called in both atomic and non-atomic
contexts, it is not always safe to lock a mutex.  Filter out all events
except the six necessary ones, which are all sleepable, before taking
the mutex.

Change-Id: I7afa567997f2f3b70b985795026ee92b90657ab5
Signed-off-by: Colin Cross <ccross@android.com>