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/plat/index.rst b/docs/plat/index.rst
index 5495280..63d29a9 100644
--- a/docs/plat/index.rst
+++ b/docs/plat/index.rst
@@ -8,10 +8,10 @@
    :hidden:
 
    allwinner
+   arm/index
    meson-gxbb
    meson-gxl
    meson-g12a
-   fvp_ve
    hikey
    hikey960
    intel-agilex
@@ -38,81 +38,19 @@
    xilinx-zynqmp
 
 This section provides a list of supported upstream *platform ports* and the
-documentation associated with them. The list of suported Arm |FVP| platforms is
-outlined in the following section.
+documentation associated with them.
 
 .. note::
    In addition to the platforms ports listed within the table of contents, there
    are several additional platforms that are supported upstream but which do not
    currently have associated documentation:
 
-   - Arm Juno Software Development Platform. Various |AArch32| and |AArch64|
-     builds of this release have been tested on r0, r1 and r2 variants of the
-     `Juno Arm Development Platform`_.
    - Arm Neoverse N1 System Development Platform (N1SDP)
    - Arm Neoverse Reference Design N1 Edge (RD-N1-Edge) FVP
    - Arm Neoverse Reference Design E1 Edge (RD-E1-Edge) FVP
    - Arm SGI-575 and SGM-775
    - MediaTek MT6795 and MT8173 SoCs
 
-Fixed Virtual Platform (FVP) Support
-------------------------------------
-
-The latest version of the AArch64 build of TF-A has been tested on the
-following Arm FVPs without shifted affinities, and that do not support threaded
-CPU cores (64-bit host machine only).
-
-.. note::
-   The FVP models used are Version 11.6 Build 45, unless otherwise stated.
-
--  ``FVP_Base_AEMv8A-AEMv8A``
--  ``FVP_Base_AEMv8A-AEMv8A-AEMv8A-AEMv8A-CCN502``
--  ``FVP_Base_RevC-2xAEMv8A``
--  ``FVP_Base_Cortex-A32x4``
--  ``FVP_Base_Cortex-A35x4``
--  ``FVP_Base_Cortex-A53x4``
--  ``FVP_Base_Cortex-A55x4+Cortex-A75x4``
--  ``FVP_Base_Cortex-A55x4``
--  ``FVP_Base_Cortex-A57x1-A53x1``
--  ``FVP_Base_Cortex-A57x2-A53x4``
--  ``FVP_Base_Cortex-A57x4-A53x4``
--  ``FVP_Base_Cortex-A57x4``
--  ``FVP_Base_Cortex-A72x4-A53x4``
--  ``FVP_Base_Cortex-A72x4``
--  ``FVP_Base_Cortex-A73x4-A53x4``
--  ``FVP_Base_Cortex-A73x4``
--  ``FVP_Base_Cortex-A75x4``
--  ``FVP_Base_Cortex-A76x4``
--  ``FVP_Base_Cortex-A76AEx4`` (Tested with internal model)
--  ``FVP_Base_Cortex-A76AEx8`` (Tested with internal model)
--  ``FVP_Base_Cortex-A77x4`` (Version 11.7 build 36)
--  ``FVP_Base_Zeusx4``
--  ``FVP_Base_Neoverse-N1x4`` (Tested with internal model)
--  ``FVP_CSS_SGI-575`` (Version 11.3 build 42)
--  ``FVP_CSS_SGM-775`` (Version 11.3 build 42)
--  ``FVP_RD_E1Edge`` (Version 11.3 build 42)
--  ``FVP_RD_N1Edge`` (Version 11.3 build 42)
--  ``Foundation_Platform``
-
-The latest version of the AArch32 build of TF-A has been tested on the
-following Arm FVPs without shifted affinities, and that do not support threaded
-CPU cores (64-bit host machine only).
-
--  ``FVP_Base_AEMv8A-AEMv8A``
--  ``FVP_Base_Cortex-A32x4``
-
-.. note::
-   The ``FVP_Base_RevC-2xAEMv8A`` FVP only supports shifted affinities.
-
-The *Foundation* and *Base* FVPs can be downloaded free of charge. See the
-`Arm FVP website`_.
-
-All the above platforms have been tested with `Linaro Release 19.06`_.
-
 --------------
 
 *Copyright (c) 2019, Arm Limited. All rights reserved.*
-
-.. _Juno Arm Development Platform: http://www.arm.com/products/tools/development-boards/versatile-express/juno-arm-development-platform.php
-.. _Arm FVP website: https://developer.arm.com/products/system-design/fixed-virtual-platforms
-.. _Linaro Release 19.06: http://releases.linaro.org/members/arm/platforms/19.06