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>

pkgs/build-support/fetchdarcs/default.nix

@@ -0,0 +1,18 @@
+{stdenvNoCC, darcs, cacert}:
+
+{url, rev ? null, context ? null, md5 ? "", sha256 ? ""}:
+
+if md5 != "" then
+  throw "fetchdarcs does not support md5 anymore, please use sha256"
+else
+stdenvNoCC.mkDerivation {
+  name = "fetchdarcs";
+  builder = ./builder.sh;
+  nativeBuildInputs = [cacert darcs];
+
+  outputHashAlgo = "sha256";
+  outputHashMode = "recursive";
+  outputHash = sha256;
+
+  inherit url rev context;
+}