x86/sev: generate SEV kernel loader hashes in x86_load_linux

x86/sev: generate SEV kernel loader hashes in x86_load_linux

If SEV is enabled and a kernel is passed via -kernel, pass the hashes of
kernel/initrd/cmdline in an encrypted guest page to OVMF for SEV
measured boot.

Co-developed-by: James Bottomley <jejb@linux.ibm.com>
Signed-off-by: James Bottomley <jejb@linux.ibm.com>
Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210930054915.13252-3-dovmurik@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>