Like nico said it would be quite difficult to do this yourself and not
really worth the time, and for the price of contracting someone else or
even spending the time yourself (vs working overtime hours) you could
buy lots of boards with already done open source firmware that works
perfectly. Literally for the price of a coreboot port for this board you
could buy 20+ fully loaded TALOS 2 systems and 50+ KCMA-D8's.

What exactly are you looking for in a board? I assume embedded? you can
pick up a coreboot compatible AM1 (check the list) for quite cheap right
now - if you require more expansion options and/or a BMC I would go with
the KCMA-D8 which supports dual fanless capable 4 or 8 core 35W TDP
CPU's and 128GB RAM - if you can find some they are a super great owner
controlled libre firmware embedded/router platform and they support
OpenBMC via a ASMB4 or ASMB5 module.
Both systems have lots of AMD provided documentation as they are from
right before when AMD stopped supporting the open source firmware
community and of course the high performance TALOS 2 is also well
documented (and has libre firmware) if you want something fast/not an
embedded platform.

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