SECURE_BOOT: Unify memory map for Layerscape based platforms

Unify memory map for Layerscape based platforms. This patch includes
changes in bootscript, bootscript header and PPA header addresses
change as per unified memory map.

Signed-off-by: Sumit Garg <sumit.garg@nxp.com>
Tested-by: Vinitha Pillai <vinitha.pillai@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>