drm/amdgpu: use the VM as job owner

For HMM we need to rework how VM synchronization works, so instead of the filp use VM as job owner.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>