Added .config_intr and .handle_interrupt callbacks.

Link event interrupt will trigger an interrupt every time when the link
goes up or down.

Signed-off-by: Radu Pirea (NXP OSS) <radu-nicolae.pirea@oss.nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>