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/development/building-parts.chapter.md

@@ -0,0 +1,74 @@
+# Building Specific Parts of NixOS {#sec-building-parts}
+
+With the command `nix-build`, you can build specific parts of your NixOS
+configuration. This is done as follows:
+
+```ShellSession
+$ cd /path/to/nixpkgs/nixos
+$ nix-build -A config.option
+```
+
+where `option` is a NixOS option with type "derivation" (i.e. something
+that can be built). Attributes of interest include:
+
+`system.build.toplevel`
+
+:   The top-level option that builds the entire NixOS system. Everything
+    else in your configuration is indirectly pulled in by this option.
+    This is what `nixos-rebuild` builds and what `/run/current-system`
+    points to afterwards.
+
+    A shortcut to build this is:
+
+    ```ShellSession
+    $ nix-build -A system
+    ```
+
+`system.build.manual.manualHTML`
+
+:   The NixOS manual.
+
+`system.build.etc`
+
+:   A tree of symlinks that form the static parts of `/etc`.
+
+`system.build.initialRamdisk` , `system.build.kernel`
+
+:   The initial ramdisk and kernel of the system. This allows a quick
+    way to test whether the kernel and the initial ramdisk boot
+    correctly, by using QEMU's `-kernel` and `-initrd` options:
+
+    ```ShellSession
+    $ nix-build -A config.system.build.initialRamdisk -o initrd
+    $ nix-build -A config.system.build.kernel -o kernel
+    $ qemu-system-x86_64 -kernel ./kernel/bzImage -initrd ./initrd/initrd -hda /dev/null
+    ```
+
+`system.build.nixos-rebuild` , `system.build.nixos-install` , `system.build.nixos-generate-config`
+
+:   These build the corresponding NixOS commands.
+
+`systemd.units.unit-name.unit`
+
+:   This builds the unit with the specified name. Note that since unit
+    names contain dots (e.g. `httpd.service`), you need to put them
+    between quotes, like this:
+
+    ```ShellSession
+    $ nix-build -A 'config.systemd.units."httpd.service".unit'
+    ```
+
+    You can also test individual units, without rebuilding the whole
+    system, by putting them in `/run/systemd/system`:
+
+    ```ShellSession
+    $ cp $(nix-build -A 'config.systemd.units."httpd.service".unit')/httpd.service \
+        /run/systemd/system/tmp-httpd.service
+    # systemctl daemon-reload
+    # systemctl start tmp-httpd.service
+    ```
+
+    Note that the unit must not have the same name as any unit in
+    `/etc/systemd/system` since those take precedence over
+    `/run/systemd/system`. That's why the unit is installed as
+    `tmp-httpd.service` here.