powerpc/86xx: Add 36-bit device tree for mpc8641hpcn

The new dts places most of the devices in physical address space
above 32-bits, which allows us to have more than 4GB of RAM present.

Signed-off-by: Becky Bruce <beckyb@kernel.crashing.org>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>