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: Ibc1762bba9fa2310a7443b4afa39c84b3b4c7534
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>
Signed-off-by: Satya Durga Srinivasu Prabhala <satyap@codeaurora.org>