net: phy: check for implementation of both callbacks in phy_drv_supports_irq

Now that the icplus driver has been fixed all PHY drivers supporting
interrupts have both callbacks (config_intr and ack_interrupt)
implemented - as it should be. Therefore phy_drv_supports_irq()
can be changed now to check for both callbacks being implemented.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>