sched: Update the wakeup placement logic for fair and rt tasks

For the fair sched class, update the select_best_cpu() policy to do
power based placement. The hope is to minimize the voltage at which
the CPU runs.

While RT tasks already do power based placement, their placement
preference has to now take into account the power cost of all tasks
on a given CPU. Also remove the check for sched_boost since
sched_boost no longer intends to elevate all tasks to the highest
capacity cluster.

Change-Id: Ic6a7625c97d567254d93b94cec3174a91727cb87
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>