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/fetchurl/boot.nix

@@ -0,0 +1,20 @@
+let mirrors = import ./mirrors.nix; in
+
+{ system }:
+
+{ url ? builtins.head urls
+, urls ? []
+, sha256
+, name ? baseNameOf (toString url)
+}:
+
+import <nix/fetchurl.nix> {
+  inherit system sha256 name;
+
+  url =
+    # Handle mirror:// URIs. Since <nix/fetchurl.nix> currently
+    # supports only one URI, use the first listed mirror.
+    let m = builtins.match "mirror://([a-z]+)/(.*)" url; in
+    if m == null then url
+    else builtins.head (mirrors.${builtins.elemAt m 0}) + (builtins.elemAt m 1);
+}