sched/fair: Consider task affinity while skipping a sched group

When placement boost is active, the CPUs in the highest capacity
sched group are only considered for task placement. The
find_best_target()->skip_sg() skips lower capacity sched groups.
This is a problem for the tasks whose affinity allows them to run
only on lower capacity sched group.

Change-Id: I935ff3dc3daa98c636885312216a68323aac3ce1
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>