sched: always do idle balance with a NEWLY_IDLE idle environment

With the introduction of energy aware scheduling, if idle_balance() is
to be called on behalf of a different CPU which is idle, CPU_IDLE is
used in the environment for load_balance(). This, however, introduces
subtle differences in load calculations and policies in the load
balancer. For example there are restrictions on which CPU is permitted
to do load balancing during !CPU_NEWLY_IDLE (see update_sg_lb_stats)
and find_busiest_group() uses different criteria to detect the
presence of a busy group. There are other differences as well. Revert
back to using the NEWLY_IDLE environment irrespective of whether
idle_balance() is called for the newly idle CPU or on behalf on
already existing idle CPU. This will ensure that task movement logic
while doing idle balance remains unaffected.

Change-Id: I388b0ad9a38ca550667895c8ed19628f3d25ce1a
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>