sched/fair: Add provision to control the spreading on SMP

Spreading the tasks across CPUs in different groups/clusters
may hurt power on some SMP systems. Start spreading the tasks
only if all the CPUs in the primary group/cluster are utilized
above sched_smp_overlap_capacity threshold.

When placement boost is active, the task is placed on the
least loaded CPU across all groups/clusters.

Change-Id: I5da67ed9230f651921bd901cbcc4e0cc55064155
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>