Documentation/devices.rst: convert it to ReST markup

- use a quote block for the big device major/minor list;
- use tables for the other device tables;
- fix the chapter/section/subsection markups;
- use ``foo`` for monotonic;
- use .. attention:: for the attention note to developers;
- use cross-references where needed;
- cleanup whitespaces;
- add it to the user's book.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>