staging: comedi: adv_pci1724: new driver

New comedi driver for Advantech PCI-1724U with modifications by Ian
Abbott <abbotti@mev.co.uk>.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmh6jj@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>