[coreboot] Fix some PCI issues on M57SLI v2

[Harald Gutmann]

Hello,

a few hours ago i started to address the PCI/PCI-E problems on the M57SLI-S4 
(rev. 2) and here is the result of the moment.

PCI-E grapic adapter works fine with the proprietary nvidia driver!
(And the GPIO configuration in cache_as_ram_auto.c should be fully corrected.)

The patch for that solution(s) is attached. (I don't know if this will work on 
v1 too, but i assume it will. I also don't know right now if there are more 
problems cleaned out with that patch.)

Please be so kindly, and don't ask why the value has changed from "68" (which 
is the same in original bios) to "A8", but recently it's necessary to do it, 
because otherwise the value is wrong when you read it out from a running 
system.

Kind Regards,
Harald