sched: actively migrate big tasks on power CPU to idle performance CPU

When performance CPU runs idle or newly idle load balancer to pull a
task on power efficient CPU, the load balancer always fails and enters
idle mode if the big task on the power efficient CPU is running.  This is
suboptimal when the running task on the power efficient CPU doesn't fit
on the power efficient CPU as it's quite possible that the big task will
sustain on the power efficient CPU until it's preempted while there is
a performance CPU sitting idle.

Revise load balancer algorithm to actively migrate big tasks on power
efficient CPU to performance CPU when performance CPU runs idle or newly
idle load balancer.

Change-Id: Iaf05e0236955fdcc7ded0ff09af0880050a2be32
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>