staging: comedi: addi_apci_3120: simplify analog output boardinfo

There are two boards supported by this driver. One with eight 14-bit analog
outputs and the other without analog outputs.

Add a bit field flag, 'has_ao', to the boardinfo and remove the 'i_NbrAoChannel'
and 'i_AoMaxdata' members. Use the new flag to determine if the analog output
subdevice needs to be initialized and open code the n_chan and maxdata.

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>