sched/fair: Code !is_big_little path into select_energy_cpu_brute()

This patch replaces the existing EAS upstream implementation of
select_energy_cpu_brute() with the one of find_best_target() used
in Android previously.

It also removes the cpumask 'and' from select_energy_cpu_brute,
see the existing use of 'cpu = smp_processor_id()' in
select_task_rq_fair().

Change-Id: If678c002efaa87d1ba3ec9989a4e9f8df98b83ec
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
[ added guarding for non-schedtune builds ]
Signed-off-by: Chris Redpath <chris.redpath@arm.com>