[M] Change in coreboot[main]: 3rdparty/open-power-signing-utils: add SecureBoot utility for OpenPOWER

[Krystian Hebel (Code Review)]

Attention is currently required from: Arthur Heymans, Elyes Haouas, Sergii Dmytruk.

Krystian Hebel has posted comments on this change by Sergii Dmytruk. ( https://review.coreboot.org/c/coreboot/+/67065?usp=email )

Change subject: 3rdparty/open-power-signing-utils: add SecureBoot utility for OpenPOWER
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Patch Set 38:

(1 comment)

Patchset:

PS38:
> What's an OS key?  The one they call a "software key"?  So just always using `sw_key_p. […]

Sorry, yes, I meant SW key. I've built the image after basically repeating
https://github.com/open-power/sb-signing-utils/blob/master/sign-with-local-k...
with `hw_key_a.key` changed to `sw_key_p.key` (no idea why it uses HW when
SW is also in that repo) and it looks correct, i.e. all signatures and keys
are in place, but obviously hash and signatures are different than in original
HBB. I'll try updating and booting later today to see if this is enough.