hw/i386/sev: Add support to encrypt BIOS when SEV-SNP is enabled

hw/i386/sev: Add support to encrypt BIOS when SEV-SNP is enabled

As with SEV, an SNP guest requires that the BIOS be part of the initial
encrypted/measured guest payload. Extend sev_encrypt_flash() to handle
the SNP case and plumb through the GPA of the BIOS location since this
is needed for SNP.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Pankaj Gupta <pankaj.gupta@amd.com>
Message-ID: <20240530111643.1091816-25-pankaj.gupta@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>