[Nouveau] nouveau_class.h

[Ben Skeggs]

So, with all the nouveau_class.h changes lately it's become rather
difficult to keep libdrm synced up with a particular mesa version.

This is much like what happens when we break our kernel ABI, but on a
far more regular basis so it has a larger impact.

I'm proposing we drop nouveau_class.h from libdrm again, and move it
back to the ddx and mesa trees where it can be updated at the same time
the code that uses it is.

Any objections / other suggestions?

Ben.