drm/amdgpu: remove entity idle timeout v2

Removing the entity from scheduling can deadlock the whole system.
Wait forever till the remaining IBs are scheduled.

v2: fix comment as well

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com> (v1)