The screen wide info such as pitch and cpp are obsoleted by the FBO
changes, so clean up the last few references to those, except for
setting up the legacy screen regions.
Putting the bufmgr in the screen is not thread-safe since the emit_reloc
changes. It also led to a significant performance hit from pthread usage
for the attempted thread-safety (up to 12% of a cpu spent on refcounting
protection in single-threaded 965). The motivation had been to allow
multi-context bufmgr sharing in classic mode, but it wasn't worth the cost.
This was replaced in previous releases of xserver/dri/libGL by reporting the
damage to the frontbuffer so that the server and driver could handle it
appropriately.
