sched: Switch to windows based load stats by default

Set window-based load stats to be the default mechanism under which
tasks get classified (as big/small) and which will drive frequency
demand for tasks.  sched_ravg_window kernel parameter can be used to
change this default setting to use PELT (per-entity load tracking)
scheme instead.

Change-Id: I626110daa0bb2b53172bedea829d31877255ceaa
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>