[coreboot] PCI MMCONF on amdfam10

[Kyösti Mälkki]

Hi

After commit 872c922 there is some trouble on PCI configuration access 
with Asus M4A785-M. This could apply to other amdfam10 too, although I 
have not yet received such reports.

As the commit message stated, I had discovered that in the beginning of 
ramstage all PCI configuration access used the IO (0xcf8) method even 
though Kconfig specified MMCONF_SUPPORT_DEFAULT which should imply all 
PCI config access is done with MMCONF unless IO is explicitly requested.

AFAICS, for all cores the MSR enabling MMCONF is programmed very early 
in the romstage. So second option for failure is there exists cases 
where IO must be used instead of MMCONF, but I could not find such 
documentation yet.

I hope Dennis can reproduce the failure log and post it in the next few 
days.

Kyösti