net: mvmdio: allow up to three clocks to be specified for orion-mdio

Allow up to three clocks to be specified and enabled for the orion-mdio
interface, which are required for this interface to be accessible on
Armada 8k platforms.

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