powerpc/corenet: CPC1 speculation disable

In PBL RAMBOOT(SPI/SD/NAND boot) mode, CPC1 used as SRAM, should disable
CPC1 speculation and keep it till relocation. Otherwise, speculation
transactions will go to DDR controller, it will cause problem.

Signed-off-by: Dave Liu <daveliu@freescale.com>
Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Acked-by: York Sun <yorksun@freescale.com>