staging: comedi: ni_mio_common: tidy up the Analog Output subdevice init

For aesthetics, add some whitespace to the Analog Output subdevice init.

Also, remove the '#ifdef PCIDMA' here and only hook up the async command
support if we have an irq and the board either has a fifo or DMA is
supported.

The ni_pcimio driver is the only place PCIDMA is defined. That driver
is also the only user of ni_mio_common that allocates devpriv->mite. Use
that test instead to determine if dma is supported.

Move 'is_67xx' check and init_ao_67xx() call into the Analog Output
subdevice init. The 67xx boards all have analog outputs and this check
does not need to be done for the boards that do not have analog outputs.

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>