net: phy: marvell10g: place in powersave mode at probe

Place the 88x3310 into powersaving mode when probing, which saves 600mW
per PHY. For both PHYs on the Macchiatobin double-shot, this saves
about 10% of the board idle power.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>