This reverts the series of commits

	67dbb4ea
	281ab031
	47807ce3

that changed the GART VM start offset.  It fixed some machines, but
seems to continually interact badly with some X versions.

Quoth Ben Herrenschmidt:

  "So I think at this point, the best is that we keep the old bogus code
   that at least is consistent with the bug in the server. I'm working on a
   big patch to X that reworks the memory map stuff completely and fixes
   those issues on the server side, I'll do a DRM patch matching this X fix
   as well so that the memory map is only ever set in one place and with
   what I hope is a correct algorithm..."
Signed-off-by: Linus Torvalds <torvalds@osdl.org>