crypto: ccp: Add the SNP_VLEK_LOAD command

When requesting an attestation report a guest is able to specify whether
it wants SNP firmware to sign the report using either a Versioned Chip
Endorsement Key (VCEK), which is derived from chip-unique secrets, or a
Versioned Loaded Endorsement Key (VLEK) which is obtained from an AMD
Key Derivation Service (KDS) and derived from seeds allocated to
enrolled cloud service providers (CSPs).

For VLEK keys, an SNP_VLEK_LOAD SNP firmware command is used to load
them into the system after obtaining them from the KDS. Add a
corresponding userspace interface so to allow the loading of VLEK keys
into the system.

See SEV-SNP Firmware ABI 1.54, SNP_VLEK_LOAD for more details.

Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Message-ID: <20240501085210.2213060-21-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>