Change in coreboot[master]: mainboard: use SeaBIOS config only when it's the payload of choice

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Change subject: mainboard: use SeaBIOS config only when it's the payload of choice
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Patch Set 2: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-gerrit/61052/ : SUCCESS

https://qa.coreboot.org/job/coreboot-checkpatch/16227/ : SUCCESS