Revert "sched: add preference for prev_cpu in HMP task placement"

Reverts commit f8d83170 temporarily
to apply the select_best_cpu() optimizations patches from a different
branch on which this commit is not available.

Change-Id: I2405733ad15c682fd1447200a62990e6bb089b33
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>