drm/amdgpu: Implement insert_end for VCE 3

drm/amdgpu: Implement insert_end for VCE 3

After a recent change VCE now hangs when VCE_CMD_END is emitted
after a pipeline sync without VM flush.
Implement insert_end to correctly insert only one VCE_CMD_END per job.

Fixes: bc639a9eadc7 ("drm/amdgpu: always emit the job vm fence")
Signed-off-by: David Rosca <david.rosca@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 8897ea8c761b856f02061848a7908040a1fe5e68)
Cc: stable@vger.kernel.org