sched: notify cpufreq on over/underprovisioned CPUs

After a migration occurs the source and destination CPUs may
not be running at frequencies which match the new task load on
those CPUs.

Previously, the scheduler was notifying cpufreq anytime a task
greater than a certain size migrates. This is suboptimal however
since this does not take into account the CPU's current
frequency and other task activity that may be present.

Change-Id: I5092bda3a517e1343f97e5a455957c25ee19b549
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>