llist: defining relaxed version of llist_empty

Defining relaxed version of llist_empty as llist_empty_relaxed,
which will be used for power-optimization.

bug 1440421

Signed-off-by: Sumit Singh <sumsingh@nvidia.com>
Reviewed-by: Sri Krishna Chowdary <schowdary@nvidia.com>
Reviewed-by: Alexander Van Brunt <avanbrunt@nvidia.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>
Signed-off-by: Chet Kener <Cl3Kener@gmail.com>

Change-Id: Iaca65c6df06282442824052d93cb0540d449a998