sched: avoid unnecessary HMP scheduler stat re-accounting

When sched_entity's runnable average changes, before and after, we
decrease and increase HMP scheduler's statistics of the sched_entity to
take into account of updated runnable average.  In that period, however,
other CPUs would see that the runnable average updating CPU's load as
less than actual.  This is suboptimal and can lead improper task placement
and load balance decision.

We can avoid such situation at least with window based load tracking as
sched_entity's load average which is for PELT won't affect to HMP
scheduler's load tracking statistics.  Thus fix to update HMP statistics
only when HMP scheduler uses PELT based load statistics.

Change-Id: I9eb615c248c79daab5d22cbb4a994f94be6a968d
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>