staging: comedi: cb_das16_cs: hookup 8254 counter subdevice

The hardware has an 8254 counter/timer to provide a pacer clock using
counters 1 and 2. Counter 0 is available to the user.

Hook up the subdevice support to allow the user to use counter 0.

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>