[coreboot] [patch] Kconfig support for M57SLI

[Harald Gutmann]

Here is my new version of the Kconfig patch for M57SLI.

It does build, but there are some warnings about CONFIG_* values not defined.

Right now I have not tested the generated images, but I think I can do that 
tomorrow.
When the images work, it will get the "Signed-off" tag.

Thanks to Myles Watson and Christi Magherusan for helping out in various 
themes according this patch and the understanding of Kconfig.

Kind regards,
Harald