Add sddm pam files

Description:

plasmalogin won't start without these files (from https://invent.kde.org/plasma/plasma-login-manager#getting-started)

sudo cp /etc/pam.d/sddm /etc/pam.d/plasmalogin
sudo cp /etc/pam.d/sddm-autologin /etc/pam.d/plasmalogin-autologin
sudo cp /etc/pam.d/sddm-greeter /etc/pam.d/plasmalogin-greeter

Additional info:

• package version(s): 6.4.git20250712-1
• config and/or log files:
• link to upstream bug report, if any:

Steps to reproduce:

1. Enable the plasmalogin service
2. Reboot
3. Boot fails because pam can't authenticate