nfp: rename the driver and add new main file

Support for the PF driver is about to be added and will share
much of the code.  When the VF driver was added we planned to
maintain the PF driver as a separate module but have decided
that for our simple use case just maintaining a single module
is more reasonable.  Rename the driver to just "nfp" and update
the Kconfig.

While at it remove latent references to NFP3200.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>