sched: Add ttwu_queue support for delayed tasks

One of the more expensive things to do is take a remote runqueue lock;
which is exactly what ttwu_runnable() ends up doing. However, in the
case of sched_delayed tasks it is possible to queue up an IPI instead.

Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250520101727.984171377@infradead.org