nixos: hardware: rename 'trackball'

Since I do intend on configuring every trackball I own to use this
scheme, not just the MX Ergo.

modules/nixos/hardware/default.nix

@@ -7,9 +7,9 @@
     ./ergodox
     ./firmware
     ./graphics
-    ./mx-ergo
     ./networking
     ./sound
+    ./trackball
     ./upower
   ];
 }

modules/nixos/hardware/trackball/default.nix

@@ -1,11 +1,11 @@
 # Hold down the `next page` button to scroll using the ball
 { config, lib, ... }:
 let
-  cfg = config.my.hardware.mx-ergo;
+  cfg = config.my.hardware.trackball;
 in
 {
-  options.my.hardware.mx-ergo = with lib; {
+  options.my.hardware.trackball = with lib; {
-    enable = mkEnableOption "MX Ergo configuration";
+    enable = mkEnableOption "trackball configuration";
   };
 
   config = lib.mkIf cfg.enable {
@@ -13,6 +13,7 @@ in
       # This section must be *after* the one configured by `libinput`
       # for the `ScrollMethod` configuration to not be overriden
       inputClassSections = lib.mkAfter [
+        # MX Ergo
         ''
           Identifier      "MX Ergo scroll button configuration"
           MatchProduct    "MX Ergo"

modules/nixos/profiles/devices/default.nix

@@ -11,7 +11,7 @@ in
     my.hardware = {
       ergodox.enable = true;
 
-      mx-ergo.enable = true;
+      trackball.enable = true;
     };
 
     # MTP devices auto-mount via file explorers