sched/fair: Set asym priority equally for all CPUs in a performance domain

All CPUs in a performance domain share the same capacity, and therefore
aren't different from one another when distinguishing between which one is
better for asymmetric packing.

Instead of unfairly prioritizing lower-numbered CPUs within the same
performance domain, treat all CPUs in a performance domain equally for
asymmetric packing.

Change-Id: Ibc18d45fabc2983650ebebec910578e26bd26809
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>