There is a device coming soon which places its port registers
somewhere different to all other Marvell switches supported so far.
Add helper functions for reading/writing port registers, making it
easier to handle this new device.
Signed-off-by: NAndrew Lunn <andrew@lunn.ch>
Reviewed-by: NVivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>