Change in coreboot[master]: nb/intel/{gm45, i945, pineview}: Use macro instead of GGC address

[Nico Huber (Code Review)]

Nico Huber has posted comments on this change. ( https://review.coreboot.org/28909 )

Change subject: nb/intel/{gm45,i945,pineview}: Use macro instead of GGC address
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Patch Set 2:
> > (1 comment)
>
> regarding the datasheet, it is 16bits.

The register read was already 16 bits. That has nothing to do with
the variable you store the value in.
> by the way, there is a conflict with this change :
> https://review.coreboot.org/#/c/coreboot/+/17645/
> so maybe I have to keep only changes related to pineview and i945.

Doesn't matter. 17645 needs an update anyway.