Staging: add comedi core

This adds the Comedi core to the staging tree.
This is a data acquision infrastructure for Linux, providing a common
interface for these types of drivers.

Taken directly from the comedi git tree, with only minor tweaks
by Greg to get it to build properly within the kernel tree.

From: David Schleef <ds@schleef.org>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Shawn Bohrer <shawn.bohrer@gmail.com>
Signed-off-by: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>