net: phy: migrate phy_init_eee() to genphy_c45_eee_is_active()

Reduce code duplicated by migrating phy_init_eee() to
genphy_c45_eee_is_active().

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>