refactor config with better structure

nixos/system/boot.nix

@@ -0,0 +1,26 @@
+{ pkgs, ... }:
+{
+  boot = {
+    kernelPackages = pkgs.linuxPackages_latest;
+
+    loader = {
+      systemd-boot.enable = true;
+      efi.canTouchEfiVariables = true;
+      # Skip the boot menu; hold Space while booting to show it.
+      timeout = 0;
+      # Keep /boot from filling up with old generations.
+      systemd-boot.configurationLimit = 5;
+    };
+
+    # Quiet boot
+    consoleLogLevel = 3;
+    initrd.verbose = false;
+    kernelParams = [
+      "quiet"
+      "udev.log_level=3"
+      "rd.udev.log_level=3"
+      "systemd.show_status=auto"
+      "rd.systemd.show_status=auto"
+    ];
+  };
+}