refactor(wpcarro/nixos): Define shared nopn.nix module

Shared between `ava` and `tarasco`. Also define `lib/default.nix` to share
utility functions like `usermod` between NixOS configurations.

Change-Id: I65b8d37520426e164c9d5f722bee4731a3c6e641
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5942
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/nixos/modules/hardware/nopn.nix

@@ -0,0 +1,52 @@
+# I tried looking up the manufacturer, product name, and version, but
+# `dmidecode -t system` reported "To be filled by O.E.M." for each of these
+# fields.
+{ config, lib, pkgs, modulesPath, ... }:
+
+{
+  imports = [
+    (modulesPath + "/installer/scan/not-detected.nix")
+  ];
+
+  fileSystems."/" = {
+    device = "/dev/disk/by-label/NIXROOT";
+    fsType = "ext4";
+  };
+
+  fileSystems."/boot" = {
+    device = "/dev/disk/by-label/NIXBOOT";
+    fsType = "vfat";
+  };
+
+  boot = {
+    initrd.availableKernelModules = [
+      "xhci_pci"
+      "ehci_pci"
+      "ahci"
+      "usb_storage"
+      "usbhid"
+      "sd_mod"
+    ];
+    initrd.kernelModules = [ ];
+    kernelModules = [ "kvm-intel" ];
+    extraModulePackages = [ ];
+
+    # Can verify these settings with:
+    # $ lsmod
+    # ...or:
+    # $ cat /etc/modprobe.d/nixos.conf
+    blacklistedKernelModules = [
+      # Disabling this buggy network driver (and preferring ethernet) to prevent
+      # my machine from becoming unresponsive.
+      # TODO(wpcarro): Consider replacing this module with this fork (if NixOS
+      # isn't already): https://github.com/tomaspinho/rtl8821ce
+      "rtw88_8821ce"
+    ];
+  };
+
+  swapDevices = [ ];
+
+  hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
+  # high-resolution display
+  hardware.video.hidpi.enable = lib.mkDefault true;
+}