Staging: comedi: add pcm3724 driver

Driver Advantech PCM-3724 card

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