sched: Ensure proper synch between isolation, hotplug, and suspend

Isolation code needs to be synchronized with both hotplug and suspend.
Ensure this by taking the lock that is taken by both paths and ensure
hotplug notifiers are processed for suspend/resume.

Change-Id: I663588cfd2f9e3972b9adc1a10887ef36cd70c57
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>