net: phy: marvell: Add support for 88e1545 PHY

The 88e1545 PHYs are discrete Marvell PHYs, found in a quad package on
the zii-devel-b board. Add support for it to the Marvell PHY driver.

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