staging: comedi: amplc_dio200: internalize 8255 DIO implementation

Implement the '8255' DIO subdevice internally to this module instead of
using the external "8255" module.  I plan to add support for additional
cards to this driver that would require the I/O callback functionality
of the 8255 module, but the existing callback functions do not have much
context to handle this elegantly.  The additional cards also have extra
DIO features which cannot be handled by the existing "8255" module and
that I'd like to support some time in the future.

The bottom line is I _could_ continue using the "8255" module for a
while with a callback function, but it would turn out to be a very ugly
callback function and I'd have to ditch the use of the "8255" module as
soon as I added an extra feature to the DIO subdevice.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>