drm/amdgpu: add destroy session when generate VCE destroy msg.

Signed-off-by: David Mao <David.Mao@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>