drm/sched: Add warning for removing hack in drm_sched_fini()

drm/sched: Add warning for removing hack in drm_sched_fini()

The assembled developers agreed at the X.Org Developers Conference 2025
that the hack added for amdgpu in drm_sched_fini() shall be removed. It
shouldn't be needed by amdgpu anymore.

As it's unclear whether all drivers really follow the life time rule of
entities having to be torn down before their scheduler, it is reasonable
to warn for a while before removing the hack.

Add a warning in drm_sched_fini() that fires if an entity is still
active.

Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patch.msgid.link/20251023123429.139848-2-phasta@kernel.org