[coreboot] Naming for identical chips with different model numbers due to different package variants

[Felix Held]

> Personally, I'd just use a little 'x' in place of D or F in this case.
What if a chip has X as suffix? At least that was my thought not to 
choose that. And that also might it can confuse people, since there is 
no NCT6776X.

I think I'll just remove the suffix from this bikeshed and add a comment 
inside the file. ;)

Regards
Felix