ttm: merge ttm_backend & ttm_tt, introduce ttm dma allocator V5

[Konrad Rzeszutek Wilk]

> > which I think was your V4 posting (or earlier) (the last patch is something I added
> > to toggle it off/on to test).
> 
> You have to allocate like a million of gem object to trigger it.
> 

Which I certainly did not, but I did find an accounting error in the
rebased v5 version of the TTM DMA that might be the culprit. Will build
a kernel shortly with those changes and see how it fares.

> >
> > The latest (V5) hit the OOM quite fast - took about an hour or two of me
> > answering emails (mutt inside gnome-terminal) and using both chrome and firefox,
> > and running a make -j10 on the Linux kernel.
> >
> > Time to turn on more debugging :-)
> >
> 
> Hhhhmm weird i did not run into that. will try to run heavy make with
> graphic along side. Does it happen without
> 0014-drm-ttm-simplify-memory-accounting-for-ttm-user.patch ?

Will try reverting it out and see what happends.