Mixed mode (-m) enables evaluation of different workload sets against one
or more load balancing strategies.

Contrary to the default mode which runs all selected workloads serialy,
mixed mode runs a second stage where they are all run in parallel. The
performance difference between the two passes is then used for the scoring
metric.

First metric is the normalized aggregate throughput, and second is
balancer "fairness" as approximated by throughput achieved in mixed mode,
relative to the best individual balancer for each workload.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>