mm, compaction: add migratetype to compact_control

mm, compaction: add migratetype to compact_control

Preparation patch.  We are going to need migratetype at lower layers
than compact_zone() and compact_finished().

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Acked-by: Johannes Weiner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>