ANDROID: sched: cpufreq: use PELT rt_rq as estimate of required RT CPU capacity

A policy of going to fmax on any RT activity will be detrimental
for power on many platforms. Often RT accounts for only a small amount
of CPU activity so sending the CPU frequency to fmax is overkill. Worse
still, some platforms may not be able to even complete the CPU frequency
change before the RT activity has already completed.

Cpufreq governors have not treated RT activity this way in the past so
it is not part of the expected semantics of the RT scheduling class. The
DL class offers guarantees about task completion and could be used for
this purpose.

Modify the schedutil algorithm to instead use the new PELT rt_rq signal
as an estimate of RT utilization of the CPU.

Based on previous work by Vincent Guittot <vincent.guittot@linaro.org>.

Change-Id: I1ed605a3e2512a94d34217a8e57c3fd97cca60be
Signed-off-by: Steve Muckle <smuckle@linaro.org>
(switched from rt_avg to PELT rt)
Signed-off-by: Chris Redpath <chris.redpath@arm.com>