net: phy: bcm7xxx: Add EPHY entry for 7712

7712 is a 16nm process SoC with a 10/100 integrated Ethernet PHY,
utilize the recently defined 16nm EPHY macro to configure that PHY.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>