[coreboot] Gigabyte M57SLI Kconfig support

[Harald Gutmann]

Hello,

here is my new patch which adds the Kconfig support for m57sli from gigabyte.

There is one Problem with the patch, but I'm not able to track that down.
I've really no idea what causes Kconfig to put all those warnings out with my 
patch. As this patch causes quite a massive amount of warnings, and I wasn't 
able to fix that it is not signed off.

The warnings which are given by make menuconfig are attached in warnings.txt 
and the patch itself is also attached.
Hopefully someone can help me to track this down.

Kind regards,
Harald