sched: Set boost policy based on sysctl_sched_is_big_little

Currently boost policy is set to SCHED_BOOST_ON_BIG when
min_possible_efficiency != max_possible_efficiency. This
does not work for a SMP system on which some CPUs have
slightly higher efficiency (for example higher cache size)
but otherwise identical to other clusters. For such systems,
spreading the tasks gives better performance under boost.

Change-Id: Ie59388cb00e2ff9777c5b89903b38015cba23b23
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>