Validate SNP Attestation Report Fields

[npmccallum]

The fields are documented on page 44 of the SNP Firmware ABI spec. They are implemented in this structure, but some fields appear to be missing and nearly all appear to be undocumented.

1. All fields from the documentation need to be accounted for (some are currently missing).
2. All fields need to be documented in the code, explaining how to validate them or why validation is unnecessary.
3. Fields that represent flags should probably use the flagset crate.
4. Whoever takes this should work with @haraldh to confirm which fields need to be validated.
5. Implement all necessary validations.

[npmccallum]

cc @rjzak

[rjzak]

• All fields from the documentation need to be accounted for (some are currently missing).
• All fields need to be documented in the code, explaining how to validate them or why validation is unnecessary.
  • Most fields documented as of commit 319b24f, but could be more detailed.
  • In the future, may want to validate against firmware versions.
• Fields that represent flags should probably use the flagset crate.
• Whoever takes this should work with @haraldh to confirm which fields need to be validated.
• Implement all necessary validations.
  • Probably should allow the last reserved field to have fields, as future revisions to the firmware may add fields, possibly before Steward can be updated to accommodate.

[rjzak]

I believe the SNP fields have been validated.

[haraldh]

we might want to reopen this