[coreboot] [PATCH] Split VIA cpu support code

[Stefan Reinauer]

The VIA CPU support code has been a bit neglected. With the upcoming
support for more C7 based systems, I changed the code to have a seperate
model_c3 and model_c7, as we have with all other cpu types.

model_c3 was simplified to catch all c3 cpus, not only the hand
maintained.

model_c7 supports correct frequency stepping for many C7 cpus.

Best wishes
  Stefan