MEDIUM: cpu-topo: change "efficiency" to consider per-core capacity

MEDIUM: cpu-topo: change "efficiency" to consider per-core capacity

This is similar to the previous change to the "performance" policy but
it applies to the "efficiency" one. Here we're changing the sorting
method to sort CPU clusters by average per-CPU capacity, and we evict
clusters whose per-CPU capacity is above 125% of the previous one.
Per-core capacity allows to detect discrepancies between CPU cores,
and to continue to focus on efficient ones as a priority.