sched: Update fair and rt placement logic to use scheduler clusters

Make use of clusters in the fair and rt scheduling classes. This is
needed as the freq domain mask can no longer be used to do correct
task placement. The freq domain mask was being used to demarcate
clusters.

Change-Id: I57f74147c7006f22d6760256926c10fd0bf50cbd
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>