migrate_pages: separate hugetlb folios migration

This is a preparation patch to batch the folio unmapping and moving for
the non-hugetlb folios.  Based on that we can batch the TLB shootdown
during the folio migration and make it possible to use some hardware
accelerator for the folio copying.

In this patch the hugetlb folios and non-hugetlb folios migration is
separated in migrate_pages() to make it easy to change the non-hugetlb
folios migration implementation.

Link: https://lkml.kernel.org/r/20230213123444.155149-3-ying.huang@intel.com


Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Bharata B Rao <bharata@amd.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>