staging: comedi: rtd520: use the pci id_table 'driver_data'

Create an enum to the boardinfo and pass that enum in the pci_driver
id_table as the driver_data.

Change the macro used to fill in the device table from PCI_DEVICE() to
PCI_VDEVICE(). This allows passing the enum as the next field.

This allows removing the 'device_id' data from the boardinfo as well the
search function that was used to locate the boardinfo for the PCI device.

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>