sched: remove the notion of small tasks and small task packing

Task packing will now be determined solely on the basis of the
power cost of task placement. All tasks are eligible for packing.
Remove the notion of "small" tasks from the scheduler.

Change-Id: I72d52d04b2677c6a8d0bc6aa7d50ff0f1a4f5ebb
Signed-off-by: Syed Rameez Mustafa <rameezmustafa@codeaurora.org>