Revert "sched/fair: correct fastpath"

This reverts commit 258cafe4. This change
was primarily done to avoid long exit idle times on mid capacity CPUs. A
task would be assigned a busy mid cap CPU if the idle one were in a deeper
idle state.

This change made sense in theory, but queueing on a busy CPU is seen to
take longer for the tasks to complete. Assigning a task to an idle CPU and
taking the idle exit latency hit has proven to be less of a bottleneck.

Change-Id: I50b27d089db4226a015e1cae6ba28c8fd4172f0c
Signed-off-by: Jonathan Avila <avilaj@codeaurora.org>