qapi/char: Make backend types properly conditional
Character backends are actually QOM types. When a backend's
compile-time conditional QOM type is not compiled in, creation fails
with "'FOO' is not a valid char driver name". Okay, except
introspecting chardev-add with query-qmp-schema doesn't work then: the
backend type is there even though the QOM type isn't.
A management application can work around this issue by using
qom-list-types instead.
Fix the issue anyway: add the conditionals to the QAPI schema.
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <
20240203080228.
2766159-4-armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>