net: usb: lan78xx: Fixup EEE

The enabling/disabling of EEE in the MAC should happen as a result of
auto negotiation. So move the enable/disable into
lan783xx_phy_link_status_change() which gets called by phylib when
there is a change in link status.

lan78xx_set_eee() now just programs the hardware with the LPI
timer value, and passed everything else to phylib, so it can correctly
setup the PHY.

lan743x_get_eee() relies on phylib doing most of the work, the
MAC driver just adds the LPI timer value.

Call phy_support_eee() to indicate the MAC does actually support EEE.

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