Revert "drm/amdgpu: fix slab-use-after-free in amdgpu_userq_mgr_fini"

This reverts commit 5fb90421.

The original patch moved `amdgpu_userq_mgr_fini()` to the driver's
`postclose` callback, which is called after `drm_gem_release()` in
the DRM file cleanup sequence.If a user application crashes or aborts
without cleaning up its user queues, 'drm_gem_release()` may free
GEM objects that are still referenced by active user queues, leading
to use-after-free. By reverting, we ensure that user queues are
disabled and cleaned up before any GEM objects are released,
preventing this class of bug. However, this reintroduces a race
during PCI hot-unplug, where device removal can race with per-file
cleanup, leading to use-after-free in suspend/unplug paths.
This will be fixed in the next patch.

Fixes: 5fb90421 ("drm/amdgpu: fix slab-use-after-free in amdgpu_userq_mgr_fini+0x70c")
Signed-off-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>