EXA patches

[Maarten Maathuis]

There is one thing that did change, driver pixmaps are not allocated
by default (only when exa deems acceleration doable). So for dri2
pixmaps you would need to create a scratch pixmap and attach a bo
afterwards. I suspect this is the issue.

About the performance, i didn't notice that, but we (nouveau) place
pixmaps in vram from the moment it's created, so this kind of approach
helps. If your driver pixmaps are different then performance may vary.

Maarten.