Pipe vs. plane fixes (hopefully third time's the charm)

[Jesse Barnes]

I'll spare you the convoluted path that got me to this point, but I 
think this set of patches atop the latest DRM, Mesa and 
xf86-video-intel trees should clear up any pipe vs. plane assumptions 
in the code.

Rather than storing the plane->pipe mapping in the SAREA, I now just 
have the DRM figure it out from the display registers.  The DDX driver 
retains its check of the DRM driver version to make sure it can handle 
the swapped plane->pipe mapping.  In this configuration (old DRM and 
new DDX) you won't see framebuffer compression on your builtin LVDS on 
pre-965 chips, but that's a small price to pay for correctness.

Patches follow, pending review (hopefully tomorrow) I'll push them 
upstream.

Thanks,
Jesse