qapi: Convert indirect uses of FOO_lookup[...] to qapi_enum_lookup()

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1503564371-26090-15-git-send-email-armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>