[coreboot] Trying to add Kconfig support for M57SLI - build error

[ron minnich]

let's slow down on these patches.

We're moving way too fast and it's getting confusing, and errors and
mistakes are creeping in. Cristi is right.

Let's first do AM2. Then nvidia south. And so on.

OK, I am going to apply Cristi's patch, and, if it looks good, commit.
Then we can do nvidia south.

ron