sched: improve logic for alerting governor

Currently we send notification to governor not taking note of cpus
that are synchronized with regard to their frequency. As a result,
scheduler could send pointless notifications (notification spam!).

Avoid this by considering synchronized cpus and alerting governor only
when the highest demand of any cpu within cluster far exceeds or falls
behind current frequency.

Change-Id: I74908b5a212404ca56b38eb94548f9b1fbcca33d
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>