edac.txt: convert EDAC documentation to ReST

Converts the EDAC driver subsystem documentation to ReST:

- Put paragraph titles in lower case;
- Add code blocks where needed;
- Convert tables to ReST markup;
- Mark filesystem and module names as verbatim;
- Adjust document to be properly displayed in html.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>