staging: comedi: ni_mio_common: tidy up DIO subdevice ifdef'ery

This file is is bit of a mess. It's included by the ni_atmio, ni_mio_cs, and
ni_pcimio drivers. The ni_pcimio driver is the only one that uses DMA. It
defines PCIDMA so that the dma code is compiled it. This causes a bunch
of ifdef'ery in the file.

The DIO subdevice for the ni_pcidio "is_m_series" boards is quite different
from the standard e-series DIO. Mainly it supports async commands that use
DMA.

Tidy up some of the ifdef'ery by adding ifdef to the subdevice init. Move
the is_m_series check to the main interrupt handler so that the unneded
handle_cdio_interrupt() can be blocked out for the ni_atmio and ni_mio_cs
drivers.

Consolidate the other ifdef's to block out the affected code.

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>