staging: comedi: dt2811: simplify analog output range options

The D/A ranges are not programmable. Currently this driver uses some
configuration options to select the comedi_lrange for each channel.
This is a bit messy and it requires the user to make sure the correct
option value is used.

The range information isn't used by the driver. The user space library
uses it to convert between raw data values and physical units. If the
user passed an incorrect option when attaching the driver the conversion
will be incorrect.

Simplify the analog output ranges by providing a range_table that
contains all the possible output ranges. The user can then select the
correct range when converting values.

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>