Commit 811b4ec7 ("qapi, target/i386/sev: Add cpu0-id to
query-sev-capabilities") wrongly stated that the new field is available
since version 7.0.

Fix the QAPI documentation to state that the cpu0-id field is included
since 7.1.

Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Message-Id: <20220420190129.3532623-1-dovmurik@linux.ibm.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>