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/from_md/configuration/customizing-packages.section.xml

@@ -0,0 +1,90 @@
+<section xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-customising-packages">
+  <title>Customising Packages</title>
+  <para>
+    Some packages in Nixpkgs have options to enable or disable optional
+    functionality or change other aspects of the package. For instance,
+    the Firefox wrapper package (which provides Firefox with a set of
+    plugins such as the Adobe Flash player) has an option to enable the
+    Google Talk plugin. It can be set in
+    <literal>configuration.nix</literal> as follows:
+    <literal>nixpkgs.config.firefox.enableGoogleTalkPlugin = true;</literal>
+  </para>
+  <warning>
+    <para>
+      Unfortunately, Nixpkgs currently lacks a way to query available
+      configuration options.
+    </para>
+  </warning>
+  <para>
+    Apart from high-level options, it’s possible to tweak a package in
+    almost arbitrary ways, such as changing or disabling dependencies of
+    a package. For instance, the Emacs package in Nixpkgs by default has
+    a dependency on GTK 2. If you want to build it against GTK 3, you
+    can specify that as follows:
+  </para>
+  <programlisting language="bash">
+environment.systemPackages = [ (pkgs.emacs.override { gtk = pkgs.gtk3; }) ];
+</programlisting>
+  <para>
+    The function <literal>override</literal> performs the call to the
+    Nix function that produces Emacs, with the original arguments
+    amended by the set of arguments specified by you. So here the
+    function argument <literal>gtk</literal> gets the value
+    <literal>pkgs.gtk3</literal>, causing Emacs to depend on GTK 3. (The
+    parentheses are necessary because in Nix, function application binds
+    more weakly than list construction, so without them,
+    <xref linkend="opt-environment.systemPackages" /> would be a list
+    with two elements.)
+  </para>
+  <para>
+    Even greater customisation is possible using the function
+    <literal>overrideAttrs</literal>. While the
+    <literal>override</literal> mechanism above overrides the arguments
+    of a package function, <literal>overrideAttrs</literal> allows
+    changing the <emphasis>attributes</emphasis> passed to
+    <literal>mkDerivation</literal>. This permits changing any aspect of
+    the package, such as the source code. For instance, if you want to
+    override the source code of Emacs, you can say:
+  </para>
+  <programlisting language="bash">
+environment.systemPackages = [
+  (pkgs.emacs.overrideAttrs (oldAttrs: {
+    name = &quot;emacs-25.0-pre&quot;;
+    src = /path/to/my/emacs/tree;
+  }))
+];
+</programlisting>
+  <para>
+    Here, <literal>overrideAttrs</literal> takes the Nix derivation
+    specified by <literal>pkgs.emacs</literal> and produces a new
+    derivation in which the original’s <literal>name</literal> and
+    <literal>src</literal> attribute have been replaced by the given
+    values by re-calling <literal>stdenv.mkDerivation</literal>. The
+    original attributes are accessible via the function argument, which
+    is conventionally named <literal>oldAttrs</literal>.
+  </para>
+  <para>
+    The overrides shown above are not global. They do not affect the
+    original package; other packages in Nixpkgs continue to depend on
+    the original rather than the customised package. This means that if
+    another package in your system depends on the original package, you
+    end up with two instances of the package. If you want to have
+    everything depend on your customised instance, you can apply a
+    <emphasis>global</emphasis> override as follows:
+  </para>
+  <programlisting language="bash">
+nixpkgs.config.packageOverrides = pkgs:
+  { emacs = pkgs.emacs.override { gtk = pkgs.gtk3; };
+  };
+</programlisting>
+  <para>
+    The effect of this definition is essentially equivalent to modifying
+    the <literal>emacs</literal> attribute in the Nixpkgs source tree.
+    Any package in Nixpkgs that depends on <literal>emacs</literal> will
+    be passed your customised instance. (However, the value
+    <literal>pkgs.emacs</literal> in
+    <literal>nixpkgs.config.packageOverrides</literal> refers to the
+    original rather than overridden instance, to prevent an infinite
+    recursion.)
+  </para>
+</section>