docs(fvp): restructure FVP platform documentation

The Arm FVP documentation has grown organically over the years. As a
result, it has become a big document, which can be difficult to digest.

Also, the organization of some of the sections does not make sense. In
particular, all "Running on the ... FVP" sections live under a section
named "Booting a preloaded kernel image (Base FVP)". To illustrate this,
here is the current table of contents:

  Arm Fixed Virtual Platforms (FVP)
    Fixed Virtual Platform (FVP) Support
    Arm FVP Platform Specific Build Options
    Booting Firmware Update images
    Booting an EL3 payload
    Booting a preloaded kernel image (Base FVP)
      Obtaining the Flattened Device Treesp
      Running on the Foundation FVP with reset to BL1 entrypoint
      Running on the AEMv8 Base FVP with reset to BL1 entrypoint
      Running on the AEMv8 Base FVP (AArch32) with reset to BL1 entrypoint
      Running on the Cortex-A57-A53 Base FVP with reset to BL1 entrypoint
      Running on the Cortex-A32 Base FVP (AArch32) with reset to BL1 entrypoint
      Running on the AEMv8 Base FVP with reset to BL31 entrypoint
      Running on the AEMv8 Base FVP (AArch32) with reset to SP_MIN entrypoint
      Running on the Cortex-A57-A53 Base FVP with reset to BL31 entrypoint
      Running on the Cortex-A32 Base FVP (AArch32) with reset to SP_MIN entrypoint

This patch breaks down this document in sub-documents, which are now
included from the index file. The table of contents (ToC) reflects the
new documents hierarchy. The depth of the ToC has been reduced to
simplify the index page. Here is what it looks like now:

  Arm Fixed Virtual Platforms (FVP)
    Fixed Virtual Platform (FVP) Support
    Arm FVP Platform Specific Build Options
    Running on the Foundation FVP
    Running on the AEMv8 Base FVP
    Running on the Cortex-A57-A53 Base FVP
    Running on the Cortex-A32 Base FVP (AArch32)
    Booting Firmware Update images
    Booting an EL3 payload
    Booting a preloaded kernel image (Base FVP)

Apart from moving information around in separate files, this patch also
makes the following minor changes to the contents:

 - Add a brief introduction about FVPs in the index page.
 - Change some of the titles names for conciseness.

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: Icb650e0ec2c7a86ccd6e7eea4e16a84c41442c96
8 files changed