tg3: Abort phy init for 5717 serdes devices

The 5717 serdes devices have a different phy register layout than all
other previous serdes devices.  This patch aborts the phy init sequence
in tg3_phy_reset() if the device is a 5717 serdes.  It also aborts the
tg3_phy_toggle_apd() operation.  Most other operations in the MII_SERDES
path are O.K.

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