Staging: comedi: new devices for ni_pcimio.c

Added PXI-6224 based on report by Romain Bossart of equivalence to PCI-6224.

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