mm: distinguish CMA and MOVABLE isolation in has_unmovable_pages()

Joonsoo has noticed that "mm: drop migrate type checks from
has_unmovable_pages" would break CMA allocator because it relies on
has_unmovable_pages returning false even for CMA pageblocks which in
fact don't have to be movable:

 alloc_contig_range
   start_isolate_page_range
     set_migratetype_isolate
       has_unmovable_pages

This is a result of the code sharing between CMA and memory hotplug
while each one has a different idea of what has_unmovable_pages should
return.  This is unfortunate but fixing it properly would require a lot
of code duplication.

Fix the issue by introducing the requested migrate type argument and
special case MIGRATE_CMA case where CMA page blocks are handled
properly.  This will work for memory hotplug because it requires
MIGRATE_MOVABLE.

Link: http://lkml.kernel.org/r/20171019122118.y6cndierwl2vnguj@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Tested-by: Ran Wang <ran.wang_1@nxp.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Yasuaki Ishimatsu <yasu.isimatu@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>