FROMLIST: sched/fair: Add is_misfit_task() function

Split it from update_misfit_status(). Use it in detach_tasks() and
update_sg_lb_wakeup_stats().

This should help us generalize misfit lb to handle more than
upmigration.

Bug: 340190651
Link: https://lore.kernel.org/lkml/20231209011759.398021-2-qyousef@layalina.io/


Change-Id: I207f36974b5f8578313b9b8a37ba68653c673976
Signed-off-by: Qais Yousef <qyousef@layalina.io>
Signed-off-by: Qais Yousef <qyousef@google.com>
[jstultz: Added lore link]
Signed-off-by: John Stultz <jstultz@google.com>