Update to (somewhat?) dendritic pattern

Heavily inspired by https://github.com/Doc-Steve/dendritic-design-with-flake-parts.

> Atomic commits? Never heard of them!

modules/hosts/keith/hardware.nix

@@ -0,0 +1,13 @@
+{ inputs, ... }: {
+  flake.modules.nixos.keith = { lib, ... }: {
+    hardware.enableRedistributableFirmware = true;
+    imports = with inputs.self.modules.nixos; [
+      amd-gpu
+    ];
+
+    boot.initrd.availableKernelModules = [ "nvme" "xhci_pci" "ahci" "usbhid" "usb_storage" "sd_mod" ];
+
+    nixpkgs.hostPlatform = "x86_64-linux";
+    hardware.cpu.amd.updateMicrocode = true;
+  };
+}