[POWERPC] bootwrapper: adds cuboot for MPC7448HPC2 platform

This patch adds cuboot support for MPC7448HPC2 platform.
The cuImage can be used with legacy u-boot without FDT support.

Signed-off-by: Roy Zang <tie-fei.zang@freescale.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>