sched/fair: Add more sched_asym_cpucapacity static branch checks

Rik noted a while back that a handful of

  sd->flags & SD_ASYM_CPUCAPACITY

& family in the CFS load-balancer code aren't guarded by the
sched_asym_cpucapacity static branch.

The load-balancer is already doing a humongous amount of work, but turning
those checks into NOPs for those who don't need it is fairly
straightforward, so do that.

Suggested-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>