sfc: Use model numbers for PHY type names

Some of the PHY type names are overly generic.  Change them to include
the model numbers of the PHYs they represent.

Correct the model number reference at the top of xfp_phy.c.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>