PowerPC: correct the SATA for p1/p2 rdb-pc platform

For p1/p2 rdb-pc platform, use the PCIe-SATA Silicon Image SATA controller.
Therefore, the SATA driver will use sata_sil, instead sata_sil3114.

Signed-off-by: Jerry Huang <Chang-Ming.Huang@freescale.com>
CC: Andy Fleming <afleming@gmail.com>