Add support for Freescale SGMII Riser Card

The 8544DS and 8572DS systems have an optional SGMII riser card which
exposes new ethernet ports which are connected to the eTSECs via an
SGMII interface.  The SGMII PHYs for this board are offset from the standard
PHY addresses, so this code modifies the passed in tsec_info structure to
use the SGMII PHYs on the card, instead.

Signed-off-by: Andy Fleming <afleming@freescale.com>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>