printk-formats.txt: standardize document format

printk-formats.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:

- add a title for the document;
- add markups for section titles;
- move authorship to the beginning and use :Author:;
- use right markup for tables;
- mark literals and literal blocks.

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