staging: comedi: cb_pcimdas: add 8254 timer (pacer) support

The hardware has an 8254 timer/counter. Channe; 0 is available as a
generic counter/timer with the clock, gate, and output signals all
availabe on the main 37 pin connector. Channels 1 and 2 are used for
the pacer.

Add 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>