[netdrvr] natsemi: minor cleanups

* make eeprom size a variable, prepping for future patch
* eliminate unused PCI_xxx stuff left over from Becker driver template
* convert a few #defines to enum
* mark PCI table const, __devinitdata
* don't bother with named constant for PCI device id

Signed-off-by: Jeff Garzik <jeff@garzik.org>