ANDROID: refactor select_task_rq_fair et al to be cleaner

We can move the energy-aware wakeup functionality around
a little and make it clear that it fits into the slow-path
wakeup code. The resulting code is a very close match to
the shape we expect to push upstream for comment.

Change-Id: Icf5a2ae9bdf6db5977240e5a1f1da2ed41e0fad7
Signed-off-by: Chris Redpath <chris.redpath@arm.com>