powerpc/85xx: Move mpc8572ds.dts to address-cells/size-cells = <2>

Change the top-level #address-cells and #size-cells to <2> so the
mpc8572ds.dts is easier to deal with both a true 32-bit physical
or 36-bit physical address space.

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