FROMLIST: sched: Add static_key for asymmetric cpu capacity optimizations

The existing asymmetric cpu capacity code should cause minimal overhead
for others. Putting it behind a static_key, it has been done for SMT
optimizations, would make it easier to extend and improve without
causing harm to others moving forward.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
[Taken from https://lore.kernel.org/lkml/1530699470-29808-2-git-send-email-morten.rasmussen@arm.com

]
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Change-Id: Iced93ffb71bb2c34eee783c585cffe7252137308