This isn't 100% as command submission via PCI-e GART buffers doesn't work.
I've hacked around that for the time being. This is essentially the code
that was used at the POWER.org event to show Bimini.
Modify the TTM backend bind arguments.
Export a number of functions needed for driver-specific super-ioctls.
Add a function to map buffer objects from the kernel, regardless of where they're
currently placed.
A number of error fixes.