mpc83xx: fix serdes setup for the MPC8378E boards

mpc83xx: fix serdes setup for the MPC8378E boards

MPC837xE specs says that SerDes1 has:

— Two lanes running x1 SGMII at 1.25 Gbps;
— Two lanes running x1 SATA at 1.5 or 3.0 Gbps.

And for SerDes2:

— Two lanes running x1 PCI Express at 2.5 Gbps;
— One lane running x2 PCI Express at 2.5 Gbps;
— Two lanes running x1 SATA at 1.5 or 3.0 Gbps.

The spec also explicitly states that PEX options are not valid for
the SD1.

Nevertheless MPC8378 RDB and MDS boards configure the SD1 for PEX,
which is wrong to do.

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