ANDROID: sched: Honor sync flag for energy-aware wakeups

Since we don't do energy-aware wakeups when we are overutilized, always
honoring sync wakeups in this state does not prevent wake-wide mechanics
overruling the flag as normal.

Having the check for (cpu_rq(cpu)->nr_running == 1) in the test condition
means that we only bypass the energy model for sync wakeups where the
cpu is about to become idle. This matches the use of this flag in Binder
which is the main place where sync wakeups come from in Android.

This patch is based upon previous work to build EAS for android products.
It replaces
commit 79e3a4a2 ("ANDROID: sched: Unconditionally honor sync flag
 for energy-aware wakeups")
in what's considered to be 'EAS'.

sync-hint code taken from wahoo
https://android.googlesource.com/kernel/msm/+/4a5e890ec60d


written by Juri Lelli <juri.lelli@arm.com>

Change-Id: I4b3d79141fc8e53dc51cd63ac11096c2e3cb10f5
Signed-off-by: Chris Redpath <chris.redpath@arm.com>
(cherry-picked from commit f1ec666a62de)
[ Moved the feature to find_energy_efficient_cpu() and removed the
  sysctl knob ]
Signed-off-by: Quentin Perret <quentin.perret@arm.com>
[ Add 'cpu_rq(cpu)->nr_running == 1' to the condition and remove the
  word 'Unconditionally' from the patch name ]
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>