sched/fair: Restructure wake_affine*() to return a CPU id

This is a preparation patch that has wake_affine*() return a CPU ID instead of
a boolean. The intent is to allow the wake_affine() helpers to be avoided
if a decision is already made. This patch has no functional change.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180130104555.4125-3-mgorman@techsingularity.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>
Change-Id: I71255e78c067ec35b81f6a20e8c161982ce34672
Signed-off-by: Yaroslav Furman <yaro330@gmail.com>
Signed-off-by: Danny Lin <danny@kdrag0n.dev>
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>