sched: Introduce scheduler boost related placement changes

Boost should:
1) Trigger tasks to run on the perf cluster whenever possible.
2) Ensure fair class placements only takes CPU load into account
3) Ensure load balance and tick makes tasks upmigrate (active)
4) Ensure RT tasks to run on big cluster for FULL_THROTTLE boost

The change corresponding to (3) will change load balance behavior
in general whereby a misfit task will always be upmigrated to the
performance cluster. This is actually the desired behavior.

Change-Id: Ifeb89e58aa1b2ecaceb988415cb145959621c983
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>