dt-bindings: correct marvell orion MDIO binding document

Correct the Marvell Orion MDIO binding document to properly reflect the
cases where an interrupt is present.  Augment the examples to show this.

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>