Switch arm64 to use the same physmem code as 32-bit arm.
The main advantage of this is to allow us to exclude memory from being used by the kernel. This may be from the memreserve property, or ranges marked as no-map under the reserved-memory node. More work is still needed to remove the physmap array. This is still used for creating the DMAP region, however other patches need to be committed before we can remove this. Obtained from: ABT Systems Ltd Sponsored by: Turing Robotic Industries