staging: comedi: adl_pci9118: support auto-attachment

Support auto-attachment of supported PCI devices by adding the
`auto_attach()` hook (`pci9118_auto_attach()`) to the `struct
comedi_driver`.  This is called via `comedi_pci_auto_attach()` at PCI
probe time.

Previously, the driver's call to `comedi_pci_auto_config()` would fall
back to the old method of auto-attaching devices and would fail because
it couldn't find a board name matching the driver name.  The new method
doesn't care about that.

There are still a few problems.  All the boards supported by this driver
have the same PCI vendor and device ID, so it will just pick the first
supported board type, "pci9118dg".  (Other supported board types have
different AI ranges or different AI speeds, but are otherwise the same.)
Also, manual attachment of devices allows several optional features to
be configured, such as use of an external multiplexord, specified
sample&hold delays and options to ignore certain hardware errors.  These
will all be set to defaults for auto-attached devices.  A future version
of the driver may address these issues via configurable device
attributes.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>