completely rework the dma_resv semantic

[Christian König]

Hi guys,

by now that should be a rather well known set of changes.

The basic idea is that instead of the fixed exclusive/shared classes we now
attach an usage to each fence in the dma_resv object describing how the
operation represented by the fence is using the resources protected by
the dma_resv.

I've addressed quite a bunch of comments already and I think this set has
already been discussed quite well now. As improvement to the last version
I've now added CCs for all the relevant maintainers to the patches changing
some functionality inside drivers.

Please review and comment,
Christian.