tg3: 5717: Allow serdes link via parallel detect

The 5717 serdes phy brings link up via parallel detection without any
additional help from the driver.  This patch changes the
tg3_setup_fiber_mii_phy() function to detect and allow the use of this
feature.

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>