util-linux: install PAM configuration files

Install PAM configuration files for su (with "su -" variant) and login
when the tools are enabled.
This finally fixes bug #5366 and now we can login with an util-linux
/bin/login.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>