doc: Final, pre-release fixes and updates ...

A small set of misc changes to ensure correctness before the v2.2
release tagging.

Change-Id: I888840b9483ea1a1633d204fbbc0f9594072101e
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Move platform list to the Platform Ports index page ...

The list of upstream platforms on the index page is growing
quite long, especially with all the FVP variants being listed
individually.

This patch leverages the "Platform Ports" chapter in the docs
table of contents to condense this information. Almost all
platform ports now have documentation, so the table of
contents serves as the list of upstream platforms by itself.

For those upstream platforms that do not have corresponding
documentation, the top-level "Platform Ports" page mentions
them individually. It also mentions each Arm FVP, just as
the index page did before.

Note that there is an in-progress patch that creates new
platform port documentation for the Arm Juno and Arm FVP
platforms, so this list of "other platforms" will soon be
reduced further as those platforms become part of the
table of contents as well.

Change-Id: I6b1eab8cba71a599d85a6e22553a34b07f213268
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Add more missing platforms ...

Add meson-g12a, qemu-sbsa and rpi4 to the documentation index so
that they will have their docs rendered and integrated into the
table of contents.

Change-Id: Id972bf2fee67312dd7bff29f92bea67842e62431
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Fix platform port inclusion ...

This patch:

- Adds any leftover platform ports that were not having their
  documentation built (not in the index.rst table of contents)
- Corrects a handful of RST formatting errors that cause poor
  rendering
- Reorders the list of platforms so that they are displayed
  in alphabetical order

Change-Id: If8c135a822d581c3c5c4fca2936d501ccfd2e94c
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Render Marvell platform documents ...

The documentation for Marvell platforms was not included in the
rendered document output until now because, while it was mostly
valid RST format, the files were saved with a .txt extension.

This patch corrects some RST formatting errors, creates a document
tree (index page) for the Marvell documents, and adds the Marvell
subtree to the main index.

Change-Id: Id7d4ac37eded636f8f62322a153e1e5f652ff51a
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Reformat platform port documents ...

The platform port documents are not very standardised right now and
they don't integrate properly into the document tree so:

1) Make sure each port has a proper name and title (incl. owner)
2) Correct use of headings, subheadings, etc in each port
3) Resolve any naming conflicts between documents

Change-Id: I4c2da6f57172b7f2af3512e766ae9ce3b840b50f
Signed-off-by: Paul Beesley <paul.beesley@arm.com>

doc: Move documents into subdirectories ...

This change creates the following directories under docs/
in order to provide a grouping for the content:

- components
- design
- getting_started
- perf
- process

In each of these directories an index.rst file is created
and this serves as an index / landing page for each of the
groups when the pages are compiled. Proper layout of the
top-level table of contents relies on this directory/index
structure.

Without this patch it is possible to build the documents
correctly with Sphinx but the output looks messy because
there is no overall hierarchy.

Change-Id: I3c9f4443ec98571a56a6edf775f2c8d74d7f429f
Signed-off-by: Paul Beesley <paul.beesley@arm.com>