sched: add sync wakeup recognition in select_best_cpu

If a wakeup is a sync wakeup, we need to discount the currently
running task's load from the waker's CPU as we calculate the best
CPU for the waking task to land on.

Change-Id: I00c5df626d17868323d60fb90b4513c0dd314825
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>