sched/rt: Add support for placement boost

When the placement boost is active for RT tasks, try to
find a CPU in higher capacity groups. If no such CPU is
available, fall back to the CPUs in the other groups.

Change-Id: I5a0edef592a72bee2f4bcca22a13ce7066972725
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>