doc: Split the User Guide into multiple files

The User Guide document has grown organically over time and
now covers a wide range of topics, making it difficult to
skim read and extract information from. Currently, it covers
these topics and maybe a couple more:

- Requirements (hardware, tools, libs)
- Checking out the repo
- Basic build instructions
- A comprehensive list of build flags
- FIP packaging
- Building specifically for Juno
- Firmware update images
- EL3 payloads
- Preloaded BL33 boot flow
- Running on FVPs
- Running on Juno

I have separated these out into a few groups that become new
documents. Broadly speaking, build instructions for the tools,
for TF-A generally, and for specific scenarios are separated.
Content relating to specific platforms (Juno and the FVPs are
Arm-specific platforms, essentially) has been moved into the
documentation that is specific to those platforms, under
docs/plat/arm.

Change-Id: Ica87c52d8cd4f577332be0b0738998ea3ba3bbec
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/perf/tsp.rst b/docs/perf/tsp.rst
new file mode 100644
index 0000000..f8b0048
--- /dev/null
+++ b/docs/perf/tsp.rst
@@ -0,0 +1,27 @@
+Test Secure Payload (TSP) and Dispatcher (TSPD)
+===============================================
+
+Building the Test Secure Payload
+--------------------------------
+
+The TSP is coupled with a companion runtime service in the BL31 firmware,
+called the TSPD. Therefore, if you intend to use the TSP, the BL31 image
+must be recompiled as well. For more information on SPs and SPDs, see the
+:ref:`firmware_design_sel1_spd` section in the :ref:`Firmware Design`.
+
+First clean the TF-A build directory to get rid of any previous BL31 binary.
+Then to build the TSP image use:
+
+.. code:: shell
+
+    make PLAT=<platform> SPD=tspd all
+
+An additional boot loader binary file is created in the ``build`` directory:
+
+::
+
+    build/<platform>/<build-type>/bl32.bin
+
+--------------
+
+*Copyright (c) 2019, Arm Limited. All rights reserved.*