staging: comedi: ni_labpc: use comedi attach_pci callback

Convert this PCI driver to use the comedi `attach_pci` callback instead
of the `attach` callback for PCI auto-configuration.  Remove support for
manual attachment of PCI boards supported by this driver.  The `attach`
callback is still needed to manually attach ISA boards, but print an
error if an attempt is made to manually attach a PCI board.

Note that this driver still uses the list of PCI "mite" devices created
by the "mite" module.  This will be dealt with by a later patch once
dynamic allocation of "mite" structures has been implemented.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>