mpc83xx: add SGMII riser module support for the MPC8378E-MDS boards

This involves configuring the SerDes and fixing up the flags and
PHY addresses for the TSECs.

For Linux we also fix up the device tree.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>