This patch declares most of the structures needed by fragmentation avoidance
and associated macros.

There are two things of note in this patch.
1. free_area_usemap is in the zone information by default and in the mem_section
for CONFIG_SPARSEMEM.  This is done to be more efficient for both memory
hotplug add and memory hotplug remove, which add and remove sections. With the
macros this placement should be transparent.

2. free_area_usemap requires > 32 bits and < 64 bits for all
known architectures and possible configurations, a compile time check has been
added to make sure future architectures still have this property.

Originally authored by Mel Gorman and heavily modified by me.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Joel Schopp <jschopp@austin.ibm.com>