net: dsa: mv88e6xxx: drop revision probing

There is no point in having a special case for the revision when probing
a switch model. The code gets cluttered with unnecessary defines, and
leads to errors when code such as mv88e6131_setup compares
PORT_SWITCH_ID_6131_B2 to ps->id which masks the revision.

Drop every revision definition, and lookup only the product number.

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>