refactor(nixos): move system config options to main nixos module

modules/nixos/hardware/audio.nix

@@ -1,9 +0,0 @@
-{ config, ... }:
-{
-  config = {
-    services.pipewire = {
-      enable = true;
-      pulse.enable = true;
-    };
-  };
-}

modules/nixos/hardware/default.nix

@@ -1,37 +1,15 @@
-{
-  lib,
-  config,
-  ...
-}:
+{ lib, ... }:
 let
   inherit (lib) singleton;
 in
 {
-  imports = [
-    ./audio.nix
-  ];
-
-  options.hardware = {
-    platform = lib.pantheon.mkStrOption;
+  config = {
+    services.fwupd.enable = true;
+    persistDirs = singleton "/var/lib/bluetooth";
+    hardware.bluetooth = {
+      enable = true;
+      settings.General.Experimental = true;
+    };
+    hardware.xone.enable = true;
   };
-
-  config = lib.mkMerge [
-    {
-      services.fwupd.enable = true;
-      persistDirs = singleton "/var/lib/bluetooth";
-      hardware.bluetooth = {
-        enable = true;
-        settings.General.Experimental = true;
-      };
-      hardware.xone.enable = true;
-    }
-    (lib.mkIf (config.hardware.platform == "amd") {
-      hardware.cpu.amd.updateMicrocode = true;
-      boot.kernelModules = [ "kvm-amd" ];
-    })
-    (lib.mkIf (config.hardware.platform == "intel") {
-      hardware.cpu.intel.updateMicrocode = true;
-      boot.kernelModules = [ "kvm-intel" ];
-    })
-  ];
 }

modules/nixos/hardware/platform/default.nix

@@ -0,0 +1,3 @@
+{
+  imports = [ ./x86_64.nix ];
+}

modules/nixos/hardware/platform/x86_64.nix

@@ -0,0 +1,18 @@
+{ config, lib, ... }:
+let
+  inherit (lib) singleton mkOption;
+  inherit (lib.types) enum;
+  cfg = config.hardware.platform;
+in
+{
+  options.hardware.platform = mkOption {
+    type = enum [
+      "amd"
+      "intel"
+    ];
+  };
+  config = {
+    hardware.cpu.${cfg}.updateMicrocode = true;
+    boot.kernelModules = singleton "kvm-${cfg}";
+  };
+}