staging: comedi: pcl818: all board types have digital inputs and outputs

All the board types have 16 digital inputs and 16 digital outputs.

Remove the 'n_dichan' and 'n_dochan' members in the boardinfo. Refactor
pcl818_attach() to always setup these subdevices.

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>