mm, compaction: rename map_pages to split_map_pages

It's non-obvious that high-order free pages are split into order-0 pages
from the function name.  Fix it.

Change-Id: I53fc91c5fc093e3fbd7e1c396fc70c061f9c21e0
Link: http://lkml.kernel.org/r/20190118175136.31341-6-mgorman@techsingularity.net


Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Rientjes <rientjes@google.com>
Cc: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 4469ab98477b290f6728b79f8d225d9d88ce16e3
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git


Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>