staging: comedi: dt282x: automatically handle D/A data format

The DT2821 series board have jumpers that set the output range for
the two Analog Output channels. The range_table for the Analog Output
subdevice provides all possible ranges to the user. When a unipolar
range is selected the board expects the data to be in a straight
binary format. When a bipolar range is select the data should be in
two's complement format.

Currently, the user passes some configuration options when attaching
to the driver to select the data format for each channel. If the
user does not pass the config options, the data format is assumed to
be straight binary.

The Analog Output subdevice now has a range_table that provides the
user will all possible ranges. Use the range information to determine
if the data values need to be munged into two's complememnt values
and deprecate the config options.

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>