T4240/eth: fix SGMII card PHY address

QSGMII card assumed to be used by default, but if SGMII card is used,
it will use different PHY address, but we don't know which card is used
until we access PHY on the card. So we check the card type slot by slot,
if we can read a PHY ID by reading a SGMII PHY address on a slot, then
the slot must have a SGMII card pluged, we mark all ports on that slot,
and fix dts to use the SGMII card PHY address when doing dts fixup
for the marked ports.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: Andy Fleming <afleming@freescale.com>