import dell optiplex 7020/9020 patch from gerrit

coreboot gerrit patch 55232, patchset 31

the actual board will be enabled in a follow-up patch.
merging the patch on its own first is better practise,
to run ./update trees -u coreboot

this way, there won't be a revision that breaks builds,
due to the idiosyncratic nature of coreboot configuration.

Signed-off-by: Leah Rowe <info@minifree.org>