staging: comedi: icp_multi: use attach_pci callback

Convert this PCI driver to use the comedi PCI auto config attach
mechanism by adding an 'attach_pci' callback function. Since the
driver does not require any external configuration options, and
the legacy 'attach' callback is now optional, remove it. The
boardinfo is also not needed now so remove it also.

This also allows removing the icp_multi.h header completely.

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