Dynamic DMA-buf locking changes

[Christian König]

Hi everyone,

since upstreaming the full dynamic DMA-buf changes turned out more problematic than previously thought I've reverted back to individual patches and separated out only the locking changes.

So this patch does NOT contain any new callbacks for pinning/unpinning and move notification, but only the locking changes necessary.

As previously discussed when the framework detects that the locking semantics between exporter and importer are different it just falls back to using a cached sgt created during attach time.

While separating the patch set I've most likely stumbled over the problem why this previously raised some lockdep warning with i915, it turned out to be just a might_lock() at the wrong place.

Please review and/or comment,
Christian.