Currently we assume non-list types when generating visitor routines for
union types. This is broken, since values like ['Type'] need to mapped
to 'TypeList'.

We already have a type_name() function to handle this that we use for
generating struct visitors, so use that here as well.
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NAmos Kong <akong@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>