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/doc/manual/administration/cleaning-store.chapter.md

@@ -0,0 +1,62 @@
+# Cleaning the Nix Store {#sec-nix-gc}
+
+Nix has a purely functional model, meaning that packages are never
+upgraded in place. Instead new versions of packages end up in a
+different location in the Nix store (`/nix/store`). You should
+periodically run Nix's *garbage collector* to remove old, unreferenced
+packages. This is easy:
+
+```ShellSession
+$ nix-collect-garbage
+```
+
+Alternatively, you can use a systemd unit that does the same in the
+background:
+
+```ShellSession
+# systemctl start nix-gc.service
+```
+
+You can tell NixOS in `configuration.nix` to run this unit automatically
+at certain points in time, for instance, every night at 03:15:
+
+```nix
+nix.gc.automatic = true;
+nix.gc.dates = "03:15";
+```
+
+The commands above do not remove garbage collector roots, such as old
+system configurations. Thus they do not remove the ability to roll back
+to previous configurations. The following command deletes old roots,
+removing the ability to roll back to them:
+
+```ShellSession
+$ nix-collect-garbage -d
+```
+
+You can also do this for specific profiles, e.g.
+
+```ShellSession
+$ nix-env -p /nix/var/nix/profiles/per-user/eelco/profile --delete-generations old
+```
+
+Note that NixOS system configurations are stored in the profile
+`/nix/var/nix/profiles/system`.
+
+Another way to reclaim disk space (often as much as 40% of the size of
+the Nix store) is to run Nix's store optimiser, which seeks out
+identical files in the store and replaces them with hard links to a
+single copy.
+
+```ShellSession
+$ nix-store --optimise
+```
+
+Since this command needs to read the entire Nix store, it can take quite
+a while to finish.
+
+## NixOS Boot Entries {#sect-nixos-gc-boot-entries}
+
+If your `/boot` partition runs out of space, after clearing old profiles
+you must rebuild your system with `nixos-rebuild boot` or `nixos-rebuild
+switch` to update the `/boot` partition and clear space.