Fixup SGMII PHY ids in the device tree

The device tree's PHY addresses need to be fixed up if we're using the
SGMII Riser Card.

The 8572, 8536, and 8544 DS boards were modified to call this function.

Code idea taken from Liu Yu <yu.liu@freescale.com>

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