docs: arm: convert docs to ReST and rename to *.rst

Converts ARM the text files to ReST, preparing them to be an
architecture book.

The conversion is actually:
  - add blank lines and identation in order to identify paragraphs;
  - fix tables markups;
  - add some lists markups;
  - mark literal blocks;
  - adjust title markups.

At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Reviewed-by Corentin Labbe <clabbe.montjoie@gmail.com> # For sun4i-ss

arch/arm/tools/mach-types

@@ -7,7 +7,7 @@
 #   http://www.arm.linux.org.uk/developer/machines/download.php
 #
 # Please do not send patches to this file; it is automatically generated!
-# To add an entry into this database, please see Documentation/arm/README,
+# To add an entry into this database, please see Documentation/arm/arm.rst,
 # or visit:
 #
 #   http://www.arm.linux.org.uk/developer/machines/?action=new