docs: namespaces: convert to ReST

Rename the namespaces documentation files to ReST, add an
index for them and adjust in order to produce a nice html
output via the Sphinx build system.

There are two upper case file names. Rename them to
lower case, as we're working to avoid upper case file
names at Documentation.

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>