qapi/qom,target/i386: sev-guest: Introduce kernel-hashes=on|off option

Introduce new boolean 'kernel-hashes' option on the sev-guest object.
It will be used to to decide whether to add the hashes of
kernel/initrd/cmdline to SEV guest memory when booting with -kernel.
The default value is 'off'.

Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Acked-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>