mm/memory_hotplug: Add hot-added memory blocks to ZONE_MOVABLE type

When onlining memory blocks, this option helps to add the target
memory block to ZONE_MOVABLE zone type. For successful offlining,
these memory blocks should belong to 'ZONE_MOVABLE' since it carries
only movable pages. When this option is not set, the default zone
policy is to add the blocks to 'ZONE_NORMAL' which may pin pages.

Change-Id: I7f38a07d3c6817141ec8cce3a910fa7d7d91712d
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>