- Resolve trivial context conflicts from dl_server clearing being moved
  around.

- Add @next to put_prev_task_scx() and @prev to pick_next_task_scx() to
  match sched/core.

- Merge sched_class->switch_class() addition from sched_ext with
  tip/sched/core changes in __pick_next_task().

- Make pick_next_task_scx() call put_prev_task_scx() to emulate the previous
  behavior where sched_class->put_prev_task() was called before
  sched_class->pick_next_task().

While this makes sched_ext build and function, the behavior is not in line
with other sched classes. The follow-up patches will address the
discrepancies and remove sched_class->switch_class().
Signed-off-by: Tejun Heo <tj@kernel.org>