sched: add preference for prev and sibling CPU in RT task placement

Add a bias towards the RT task's previous CPU and sibling CPUs in order
to avoid cache bouncing and migrations.

CRs-fixed: 927903
Change-Id: I45d79d774e65efcb38282130b6692b4c3b03c2f0
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>