ANDROID: sched: Introduce Window Assisted Load Tracking (WALT)

This patch is a combination of many many patches which have
been previously applied to Android/EAS kernels. Similarly to
other EAS components, we are squashing these to present a more
orderly view of component history and relationships.

The original description of WALT was:

Use a window based view of time in order to track task demand
and CPU utilization in the scheduler.

WALT accounts two major statistics; CPU load and cumulative tasks
demand.

The CPU load which is account of accumulated each CPU's absolute
execution time is for CPU frequency guidance.  Whereas cumulative
tasks demand which is each CPU's instantaneous load to reflect
CPU's load at given time is for task placement decision.

Use cumulative tasks demand for cpu_util() for task placement and
introduce cpu_util_freq() for frequency guidance.

This version includes the "cumulative window demand" statistic
which was originally described as:

Energy cost estimation has been a long lasting challenge for WALT
because WALT guides CPU frequency based on the CPU utilization of
previous window.  Consequently it's not possible to know newly
waking-up task's energy cost until WALT's end of the current window.

The WALT already tracks 'Previous Runnable Sum' (prev_runnable_sum)
and 'Cumulative Runnable Average' (cr_avg).  They are designed for
CPU frequency guidance and task placement but unfortunately both
are not suitable for the energy cost estimation.

It's because using prev_runnable_sum for energy cost calculation would
make us to account CPU and task's energy solely based on activity in the
previous window so for example, any task didn't have an activity in the
previous window will be accounted as a 'zero energy cost' task.
Energy estimation with cr_avg is what energy_diff() relies on at present.
However cr_avg can only represent instantaneous picture of energy cost
thus for example, if a CPU was fully occupied for an entire WALT window
and became idle just before window boundary, and if there is a wake-up,
energy_diff() accounts that CPU is a 'zero energy cost' CPU.

As a result, introduce a new accounting unit 'Cumulative Window Demand'.
The cumulative window demand tracks all the tasks' demands have seen in
current window which is neither instantaneous nor actual execution time.
Because task demand represents estimated scaled execution time when the
task runs a full window, accumulation of all the demands represents
predicted CPU load at the end of window.

Thus we can estimate CPU's frequency at the end of current WALT window
with the cumulative window demand.

This version is extracted wholesale from the version currently
available in android-4.4 and android-4.9.

Window Assisted Load Tracking (WALT) implementation credits:
 Srivatsa Vaddagiri, Steve Muckle, Syed Rameez Mustafa,
 Joonwoo Park, Pavan Kumar Kondeti, Olav Haugan,
 Srinath Sridharan, Vikram Mulukutla, Todd Kjos, Juri Lelli,
 John Stultz, Andres Oportus

Change-Id: If92dd9db843374073be59d2cb83febfef993b562
Signed-off-by: Chris Redpath <chris.redpath@arm.com>