sched: EAS: allow newly idle load balancing selectively

At present EAS disallows all load balancers including newly idle load
balancer until system's marked as over utilized.

However load balancer is very good opportunity point from both power
and performance perspective.  Especially newly idle load balancer
gives the most benefits as the idle balancing CPU is idle in CPU load
aspect and it's already out of low power mode so wake up latency is
minimal.  Hence there are very seldom cases doing idle balancing has
downside.  One possible negative impact it can bring is possible
frequency increase when the balancing CPU already executed more than
cpufreq's capacity margin whereas the busy CPU didn't.  In such case
pulling task to newly idle CPU will cause higher CPU frequency.

With WALT, however, scheduler can project CPU frequency before and
after the load balancing with cumulative window demand.  Therefore
it can selectively migrate tasks only when doing such won't increase
CPU's frequency or when doing such will decrease source CPU's
frequency.

Allow newly idle load balancer selectively.  This will be beneficial
both for power and performance.

Change-Id: I7a763e9d1c6927730cb84d9fca91d232cd1a35a5
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>