net: mv643xx_eth: properly start/stop phy device

When using phydev, it should be phy_start/phy_stop'ed properly. This
driver doesn't do that, so add the corresponding calls to port_start/
stop respectively.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Acked-by: Mugunthan V N <mugunthanvnm@ti.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>