Input: convert event codes documentation into ReST format

This file require minimum adjustments to be a valid ReST file.
Do it, in order to be able to parse it with Sphinx.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>