net: dsa: mv88e6xxx: Add helper for accessing port registers

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

drivers/net/dsa/mv88e6xxx/mv88e6xxx.h

@@ -37,7 +37,6 @@
 #define ADDR_SERDES		0x0f
 #define SERDES_PAGE_FIBER	0x01
 
-#define REG_PORT(p)		(0x10 + (p))
 #define PORT_STATUS		0x00
 #define PORT_STATUS_PAUSE_EN	BIT(15)
 #define PORT_STATUS_MY_PAUSE	BIT(14)