Enforce dma_fence container rules

[Christian König]

Hi Daniel,

second version of this set.

I've kept the fence ops exported for now since there are indeed valid uses in the drm_syncobj implementation which needs a more wider rework.

But quite a bunch of cases in i915, one in amdgpu and another one in vmwgfx are cleaned up at the end of this series now.

Please review and comment,
Christian.