staging: comedi: dac02: introduce comedi driver for DAC02 boards

This board is currently supported by the poc driver. That driver used
to support a number of simple boards but now only provides support for
the DAC02 board.

Introduce a new comedi driver specifically for the DAC02 board. This
allows cleaning up all the cruft.

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>