staging: comedi: daqboard2000: redo DAC control register macros

Rename the macros used to define values for the DAC control register to
avoid CamelCase and to make it clearer which register they are
associated with.  Refactor the macros used to define values to enable or
disable DAC channels to use the channel number as a parameter.  None of
these macros are currently used by the driver.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>