staging: comedi: ni_at_a2150: convert driver to use the comedi_8254 module

The hardware supported by this driver includes an 8254 timer. For aesthetics,
convert it to use the comedi_8254 module to provide support for the 8254 timer.

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>