powerpc/bootwrapper: Custom build options for XPedite52xx targets

Some XPedite52xx boards have a legacy boot loader requiring some special
care in the boot wrapper.  The use of cuboot-85xx is needed to fix
up embedded device trees, and a custom link address is specified to
accommodate the boot loader and larger kernel image sizes used on X-ES
MPC85xx platforms.

Signed-off-by: Nate Case <ncase@xes-inc.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>