staging: comedi: comedi_parport: tidy up the register map

Rename the register map defines to better describe the hardware.

Add defines for the control register bits that enable the irq and
change the direction of the data register. This gets rid of the
"magic" numbers.

Remove PARPORT_SIZE, it's only used when requesting the i/o region
with comedi_request_region().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>