tg3 is coded to refuse to attach to 5717 serdes devices.  Now that the
hardware is better supported, we can relax this restriction.  This patch
also fixes a recently introduced bug which will cause serdes parallel
detection not to work with 5780 class devices.
Signed-off-by: Matt Carlson <mcarlson@broadcom.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>