mm/migrate: rename migration reason MR_CMA to MR_CONTIG_RANGE

mm/migrate: rename migration reason MR_CMA to MR_CONTIG_RANGE

alloc_contig_range() initiates compaction and eventual migration for the
purpose of either CMA or HugeTLB allocations.  At present, the reason
code remains the same MR_CMA for either of these cases.  Let's make it
MR_CONTIG_RANGE which will appropriately reflect the reason code in both
these cases.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Anshuman Khandual <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>