nfp: add support for reporting CRC32 hash function

Some firmware images may reuse CRC32 hardware to compute RXHASH.
Make sure we report the correct hash function.  Note that we don't
support changing functions at runtime.  That would also require
a few more additions to the way the key is set because different
functions have different key sizes.

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