sched/fair: Remove idle_balance() declaration in sched.h

Remove idle_balance() from the public life; also reduce some #ifdef
clutter by folding the pick_next_task_fair() idle path into
idle_balance().

Cc: mingo@kernel.org
Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140211151148.GP27965@twins.programming.kicks-ass.net


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>