uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

nixos/modules/virtualisation/digital-ocean-image.nix

@@ -0,0 +1,70 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+let
+  cfg = config.virtualisation.digitalOceanImage;
+in
+{
+
+  imports = [ ./digital-ocean-config.nix ];
+
+  options = {
+    virtualisation.digitalOceanImage.diskSize = mkOption {
+      type = with types; either (enum [ "auto" ]) int;
+      default = "auto";
+      example = 4096;
+      description = ''
+        Size of disk image. Unit is MB.
+      '';
+    };
+
+    virtualisation.digitalOceanImage.configFile = mkOption {
+      type = with types; nullOr path;
+      default = null;
+      description = ''
+        A path to a configuration file which will be placed at
+        <literal>/etc/nixos/configuration.nix</literal> and be used when switching
+        to a new configuration. If set to <literal>null</literal>, a default
+        configuration is used that imports
+        <literal>(modulesPath + "/virtualisation/digital-ocean-config.nix")</literal>.
+      '';
+    };
+
+    virtualisation.digitalOceanImage.compressionMethod = mkOption {
+      type = types.enum [ "gzip" "bzip2" ];
+      default = "gzip";
+      example = "bzip2";
+      description = ''
+        Disk image compression method. Choose bzip2 to generate smaller images that
+        take longer to generate but will consume less metered storage space on your
+        Digital Ocean account.
+      '';
+    };
+  };
+
+  #### implementation
+  config = {
+
+    system.build.digitalOceanImage = import ../../lib/make-disk-image.nix {
+      name = "digital-ocean-image";
+      format = "qcow2";
+      postVM = let
+        compress = {
+          "gzip" = "${pkgs.gzip}/bin/gzip";
+          "bzip2" = "${pkgs.bzip2}/bin/bzip2";
+        }.${cfg.compressionMethod};
+      in ''
+        ${compress} $diskImage
+      '';
+      configFile = if cfg.configFile == null
+        then config.virtualisation.digitalOcean.defaultConfigFile
+        else cfg.configFile;
+      inherit (cfg) diskSize;
+      inherit config lib pkgs;
+    };
+
+  };
+
+  meta.maintainers = with maintainers; [ arianvp eamsden ];
+
+}