Move filesystems to system folder.

nodes/hosts/lappy/configuration.nix

@@ -8,9 +8,9 @@
   imports =
     [ # Include the results of the hardware scan.
       ./hardware-configuration.nix
-      ./filesystems.nix
       ./programs/sof-firmware.nix
       ./services/touchpad.nix
+      ./system/filesystems.nix
       ./system/networking.nix
     ];