powerpc/mpc85xx:Disable non DDR LAWs before init_law

Before parsing LAW table i.e. init_law, boot loader should disable all
previous LAWs except DDR LAWs which has been created by previous
pre boot loader during DDR initialization.

Signed-off-by: Prabhakar Kushwaha <prabhakar@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>