[coreboot] Mptable fix for M57SLI

[Harald Gutmann]

Hello,

I've given it another try to fix the mptable of the M57SLI.

The attached patch fixes for me the following things:
    * Nvidia graphic device works on PCIe-16x slot (black).
    * Both PCI cards in the two available slots work fine.
    * Also the PCIe 1x slots should work fine. (untested)

It would be fine if someone of you could test and verify if that patch works on 
hardware revision v1 too.

I hope that this fixes all the problems along with interrupts for this 
mainboard and I'm looking forward that someone can verify/test this.

Kind regards,
Harald

PS: Is it necessary to add PCI_INT for 00:08/07.01-03?