Staging: comedi: add poc driver

mini-drivers for POC (Piece of crap) boards.  Currently
supports:
	Keithley Metrabyte DAC-02
	Advantech PCL-733, PCL-734

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