Currently, there is no privilege separation of the SEV command; you can
run them all or none of them. This is less than ideal because it means
that a compromise of the code which launches VMs could make permanent
change to the SEV certifcate chain which will affect others.

These commands are required to attest the VM environment:
 - SEV_PDH_CERT_EXPORT
 - SEV_PLATFORM_STATUS
 - SEV_GET_{ID,ID2}

These commands manage the SEV certificate chain:
 - SEV_PEK_CERR_IMPORT
 - SEV_FACTORY_RESET
 - SEV_PEK_GEN
 - SEV_PEK_CSR
 - SEV_PDH_GEN

Lets add the CAP_SYS_ADMIN check for the group of the commands which alters
the SEV certificate chain to provide some level of privilege separation.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Gary Hook <gary.hook@amd.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Tom Lendacky <Thomas.Lendacky@amd.com>
Tested-by: David Rientjes <rientjes@google.com>
Co-developed-by: David Rientjes <rientjes@google.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>