Fence array patchset

[Christian König]

Hi guys,

this is the next iteration of the fence array patch set.

Daniel suggested that I provide an example on how this functionality might be
used by a driver. So I added a few additional patches in this series to show
what I want to do with this in the amdgpu driver.

The main idea is that for each VMID we have a set of hardware fences which are
currently using this VMID. Now when a new command submission needs a VMID we
construct a fence array which should signal when any of the VMIDs becomes
available and gives that back to our the scheduler.

This effort and my testing also found a rather stupid typo in the code and I
also tried to incorporate the comments from Chris and Daniel as well.

I think it's ready to land now, but as usual feel free to take it apart.

Cheers,
Christian.