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/tasks/bcache.nix

@@ -0,0 +1,23 @@
+{ config, lib, pkgs, ... }:
+
+{
+  options.boot.initrd.services.bcache.enable = (lib.mkEnableOption "bcache support in the initrd") // {
+    visible = false; # only works with systemd stage 1
+  };
+
+  config = {
+
+    environment.systemPackages = [ pkgs.bcache-tools ];
+
+    services.udev.packages = [ pkgs.bcache-tools ];
+
+    boot.initrd.extraUdevRulesCommands = lib.mkIf (!config.boot.initrd.systemd.enable) ''
+      cp -v ${pkgs.bcache-tools}/lib/udev/rules.d/*.rules $out/
+    '';
+
+    boot.initrd.services.udev = lib.mkIf config.boot.initrd.services.bcache.enable {
+      packages = [ pkgs.bcache-tools ];
+      binPackages = [ pkgs.bcache-tools ];
+    };
+  };
+}