fix(rpi4): set up GPU support

hardware/gpu-rpi4.nix

@@ -0,0 +1,19 @@
+{ config, pkgs, ... }:
+
+{
+  hardware.opengl = {
+    enable = true;
+    setLdLibraryPath = true;
+    package = pkgs.mesa_drivers;
+  };
+  hardware.deviceTree = {
+    overlays = [ "${pkgs.device-tree_rpi.overlays}/vc4-fkms-v3d.dtbo" ];
+  };
+  services.xserver = {
+    enable = false;
+    videoDrivers = [ "modesetting" ];
+  };
+  boot.loader.raspberryPi.firmwareConfig = ''
+    gpu_mem=192
+  '';
+}

rpi4.nix

@@ -3,6 +3,7 @@
 with builtins; {
   imports = [
     # ./hardware/base.nix
+    ./hardware/gpu-rpi4.nix
     # ./system
     ./system/nix.nix
     ./system/i18n.nix