nixos/displayManager: make autoLogin options independent of DM type

Co-authored-by: volth <volth@volth.com>

nixos/modules/installer/cd-dvd/installation-cd-graphical-gnome.nix

@@ -11,15 +11,17 @@ with lib;
 
   services.xserver.desktopManager.gnome3.enable = true;
 
-  services.xserver.displayManager.gdm = {
-    enable = true;
-    # autoSuspend makes the machine automatically suspend after inactivity.
-    # It's possible someone could/try to ssh'd into the machine and obviously
-    # have issues because it's inactive.
-    # See:
-    # * https://github.com/NixOS/nixpkgs/pull/63790
-    # * https://gitlab.gnome.org/GNOME/gnome-control-center/issues/22
-    autoSuspend = false;
+  services.xserver.displayManager = {
+    gdm = {
+      enable = true;
+      # autoSuspend makes the machine automatically suspend after inactivity.
+      # It's possible someone could/try to ssh'd into the machine and obviously
+      # have issues because it's inactive.
+      # See:
+      # * https://github.com/NixOS/nixpkgs/pull/63790
+      # * https://gitlab.gnome.org/GNOME/gnome-control-center/issues/22
+      autoSuspend = false;
+    };
     autoLogin = {
       enable = true;
       user = "nixos";

nixos/modules/installer/cd-dvd/installation-cd-graphical-plasma5.nix

@@ -16,8 +16,8 @@ with lib;
     };
 
     # Automatically login as nixos.
-    displayManager.sddm = {
-      enable = true;
+    displayManager = {
+      sddm.enable = true;
       autoLogin = {
         enable = true;
         user = "nixos";