[S] Change in coreboot[master]: mb/google/volteer: Add VBT data files for variants

[Sean Rhodes (Code Review)]

Attention is currently required from: Matt DeVillier, Nick Vaccaro.

Sean Rhodes has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/74852 )

Change subject: mb/google/volteer: Add VBT data files for variants
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Patch Set 2: Code-Review+1

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/74852/comment/1101094e_5e2dd39f 
PS2, Line 10: Several boards use the same VBT, so put it under
            : the baseboard and make it the default; 
Found that hard to read, maybe:
- Place the common VBT under the baseboard directory and set it as the default
- For variants with a unique VBT, override the default and use the file in their respective directories