trenchboot.org documentation update

[krystian-hebel]

Update the existing PoC described at https://trenchboot.org/blueprints/AMD_coreboot_DRTM_payload/ and reframe it as a use case.

• Update with new implementation details.
• Add Intel section (or new file, depending on number of differences).
• If the implementation requires changes to SLRT or other parts of the specification, it should also be updated.

Form: PR to https://github.com/TrenchBoot/TrenchBoot.github.io