sched: continue to search less power efficient cpu for load balancer

When choosing a CPU to do power-aware active balance from the load
balancer currently selects the first eligible CPU it finds, even if
there is another eligible CPU which is higher-power. This can lead to
suboptimal load balancing behavior and extra migrations. Power and
performance will be impacted.

Achieve better power and performance by continuing to search the least
power efficient cpu as long as the cpu's load average is higher than or
equal to the busiest cpu found by far.

CRs-fixed: 777341
Change-Id: I14eb21ab725bf7dab88b2e1e169aced6f2d712ca
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>