crypto: ccp - Add DOWNLOAD_FIRMWARE SEV command

The DOWNLOAD_FIRMWARE command, added as of SEV API v0.15, allows the OS
to install SEV firmware newer than the currently active SEV firmware.

For the new SEV firmware to be applied it must:
* Pass the validation test performed by the existing firmware.
* Be of the same build or a newer build compared to the existing firmware.

For more information please refer to "Section 5.11 DOWNLOAD_FIRMWARE" of
https://support.amd.com/TechDocs/55766_SEV-KM%20API_Specification.pdf

Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>