variant: make script work for boards with different coreboot reference

Ambassador program uses --board=ambassador, but uses the Puff templates
as its coreboot reference. This change adds support for separate
coreboot_reference, with a fallback to board for configs that don't set
a separate coreboot reference.

TEST=Ran end-to-end to create a variant for genesis

Change-Id: Ib061430d9770b73165c4bf78b809607f91f25718
Reviewed-by: Paul Fagerburg <>
Commit-Queue: Matthew Ziegelbaum <>
Tested-by: Matthew Ziegelbaum <>
1 file changed