sched/fair: Add lag based placement

With the introduction of avg_vruntime, it is possible to approximate
lag (the entire purpose of introducing it in fact). Use this to do lag
based placement over sleep+wake.

Specifically, the FAIR_SLEEPERS thing places things too far to the
left and messes up the deadline aspect of EEVDF.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230531124603.794929315@infradead.org