Hi, you might want do give Option "VBERestore" "true" in the Device Section a try.see i810(4) manpage for details. This Option causes lockups with certain Bioses, so be warned...
Sidenote: you have dri enabled in your XF86Config, but force the chipset to use only 8192kB VideoMem later.
This won't work... Comment out your VideoMem Line. cheers. Christian