[PATCH] new radeon memory map fixes (#3)

[Benjamin Herrenschmidt]

Here's a 3rd set of patches. Please report regressions ASAP as I intend
to merge those in the various CVS trees real soon now.

I fixed a couple of possible segfaults I found due to initialisation
issues (places relying on pScrn->pScreen from within ScreenInit() and
incorrect ordering of colormap vs. cursor inits for example).
 
Also, I fixed a potential issue in the DRM with machines where AGP
writeback doesn't work (we would still rely on AGP writeback for the
ring read ptr instead of reading it from a register).

Patches are at:

Xorg driver patch:
http://gate.crashing.org/~benh/radeon-memmap-7.0-3.diff

DRM patch:
http://gate.crashing.org/~benh/radeon-memmap-drm-4.diff

Cheers,
Ben.