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/lib/eval-cacheable-options.nix

@@ -0,0 +1,53 @@
+{ libPath
+, pkgsLibPath
+, nixosPath
+, modules
+, stateVersion
+, release
+}:
+
+let
+  lib = import libPath;
+  modulesPath = "${nixosPath}/modules";
+  # dummy pkgs set that contains no packages, only `pkgs.lib` from the full set.
+  # not having `pkgs.lib` causes all users of `pkgs.formats` to fail.
+  pkgs = import pkgsLibPath {
+    inherit lib;
+    pkgs = null;
+  };
+  utils = import "${nixosPath}/lib/utils.nix" {
+    inherit config lib;
+    pkgs = null;
+  };
+  # this is used both as a module and as specialArgs.
+  # as a module it sets the _module special values, as specialArgs it makes `config`
+  # unusable. this causes documentation attributes depending on `config` to fail.
+  config = {
+    _module.check = false;
+    _module.args = {};
+    system.stateVersion = stateVersion;
+  };
+  eval = lib.evalModules {
+    modules = (map (m: "${modulesPath}/${m}") modules) ++ [
+      config
+    ];
+    specialArgs = {
+      inherit config pkgs utils;
+    };
+  };
+  docs = import "${nixosPath}/doc/manual" {
+    pkgs = pkgs // {
+      inherit lib;
+      # duplicate of the declaration in all-packages.nix
+      buildPackages.nixosOptionsDoc = attrs:
+        (import "${nixosPath}/lib/make-options-doc")
+          ({ inherit pkgs lib; } // attrs);
+    };
+    config = config.config;
+    options = eval.options;
+    version = release;
+    revision = "release-${release}";
+    prefix = modulesPath;
+  };
+in
+  docs.optionsNix