sched: Trying to reduce power usage

Using macros cpu_relaxed_read, cpu_relaxed_read_long and
cpu_read_relax in core.c to improve power efficiency.

Bug 1440421

Change-Id: Ic49b88fa6fb0cb847fed49886b2865bed72203db
Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-on: http://git-master/r/368841
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Bharat Nihalani <bnihalani@nvidia.com>
Tested-by: Bharat Nihalani <bnihalani@nvidia.com>