staging: comedi: aio_aio12_8: hookup 8254 counter/timer

This board has an industry-standard 8254 chip with the gate, clock,
and output pins for each counter available on the connector.

Hookup the 8254 counter as a comedi subdevice.

Provice an (*insn_config) for the user to query the clock source
for each channel.

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>