Intel-IOMMU.txt: standardize document format

Intel-IOMMU.txt: standardize document format

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

This file is almost in the right format. It only needed to
convert a list to bulleted list and to use the right markup
for literal blocks.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>