net: dsa: mv88e6xxx: add family to info

Add an mv88e6xxx_family enum to the info structure for better family
indentification.

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>