net: dsa: mv88e6352: Use mnemonics for EEPROM registers and bits

Add register definitions #defines for accessing the EEPROM.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: David S. Miller <davem@davemloft.net>