staging: comedi: cb_pcidas: refactor analog output boardinfo

Only some of the boards supported by this driver have analog outputs
but they always have 2 channels. Refactor the 'ao_nchan' member of
the boardinfo into a bit-field flag 'has_ao' to save a bit of space.
Also, convert the 'has_ao_fifo' member into a bit-field flag.

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>