staging: comedi: skel: 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 'devid' data from the boardinfo as well the
search function that was used to locate the boardinfo for the PCI
device.

Cleanup some of the comments to describe the usage of the 'context'
in the (*auto_attach).

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>