tg3: Allow GPHY powerdown on 5761

The ENABLE_APE flag tells the driver whether or not the device has an
Application Processing Engine (APE).  The APE does not need the PHY to
be powered unless it is running management firmware.  For backwards
compatibility, management firmware will still set the ENABLE_ASF bit.
Consequently, there is no reason to consider the ENABLE_APE flag when
deciding whether or not to power down the phy.

Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>