PAM: use user name hint if any domain has set it
When using multiple domains the user name hint should be shown even if
only one domain has set the flag to have a consistent user experience.
Currently this would only be related to logins with GDM and activated
GDM Smartcard plugin.
Related to https://pagure.io/SSSD/sssd/issue/3949
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>