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/development/building-parts.chapter.xml

@@ -0,0 +1,124 @@
+<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-building-parts">
+  <title>Building Specific Parts of NixOS</title>
+  <para>
+    With the command <literal>nix-build</literal>, you can build
+    specific parts of your NixOS configuration. This is done as follows:
+  </para>
+  <programlisting>
+$ cd /path/to/nixpkgs/nixos
+$ nix-build -A config.option
+</programlisting>
+  <para>
+    where <literal>option</literal> is a NixOS option with type
+    <quote>derivation</quote> (i.e. something that can be built).
+    Attributes of interest include:
+  </para>
+  <variablelist>
+    <varlistentry>
+      <term>
+        <literal>system.build.toplevel</literal>
+      </term>
+      <listitem>
+        <para>
+          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 <literal>nixos-rebuild</literal>
+          builds and what <literal>/run/current-system</literal> points
+          to afterwards.
+        </para>
+        <para>
+          A shortcut to build this is:
+        </para>
+        <programlisting>
+$ nix-build -A system
+</programlisting>
+      </listitem>
+    </varlistentry>
+    <varlistentry>
+      <term>
+        <literal>system.build.manual.manualHTML</literal>
+      </term>
+      <listitem>
+        <para>
+          The NixOS manual.
+        </para>
+      </listitem>
+    </varlistentry>
+    <varlistentry>
+      <term>
+        <literal>system.build.etc</literal>
+      </term>
+      <listitem>
+        <para>
+          A tree of symlinks that form the static parts of
+          <literal>/etc</literal>.
+        </para>
+      </listitem>
+    </varlistentry>
+    <varlistentry>
+      <term>
+        <literal>system.build.initialRamdisk</literal> ,
+        <literal>system.build.kernel</literal>
+      </term>
+      <listitem>
+        <para>
+          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 <literal>-kernel</literal> and
+          <literal>-initrd</literal> options:
+        </para>
+        <programlisting>
+$ 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
+</programlisting>
+      </listitem>
+    </varlistentry>
+    <varlistentry>
+      <term>
+        <literal>system.build.nixos-rebuild</literal> ,
+        <literal>system.build.nixos-install</literal> ,
+        <literal>system.build.nixos-generate-config</literal>
+      </term>
+      <listitem>
+        <para>
+          These build the corresponding NixOS commands.
+        </para>
+      </listitem>
+    </varlistentry>
+    <varlistentry>
+      <term>
+        <literal>systemd.units.unit-name.unit</literal>
+      </term>
+      <listitem>
+        <para>
+          This builds the unit with the specified name. Note that since
+          unit names contain dots (e.g.
+          <literal>httpd.service</literal>), you need to put them
+          between quotes, like this:
+        </para>
+        <programlisting>
+$ nix-build -A 'config.systemd.units.&quot;httpd.service&quot;.unit'
+</programlisting>
+        <para>
+          You can also test individual units, without rebuilding the
+          whole system, by putting them in
+          <literal>/run/systemd/system</literal>:
+        </para>
+        <programlisting>
+$ cp $(nix-build -A 'config.systemd.units.&quot;httpd.service&quot;.unit')/httpd.service \
+    /run/systemd/system/tmp-httpd.service
+# systemctl daemon-reload
+# systemctl start tmp-httpd.service
+</programlisting>
+        <para>
+          Note that the unit must not have the same name as any unit in
+          <literal>/etc/systemd/system</literal> since those take
+          precedence over <literal>/run/systemd/system</literal>. That’s
+          why the unit is installed as
+          <literal>tmp-httpd.service</literal> here.
+        </para>
+      </listitem>
+    </varlistentry>
+  </variablelist>
+</chapter>