migrate_pages_batch: simplify retrying and failure counting of large folios

After recent changes to the retrying and failure counting in
migrate_pages_batch(), it was found that it's unnecessary to count
retrying and failure for normal, large, and THP folios separately. 
Because we don't use retrying and failure number of large folios directly.
So, in this patch, we simplified retrying and failure counting of large
folios via counting retrying and failure of normal and large folios
together.  This results in the reduced line number.

Previously, in migrate_pages_batch we need to track whether the source
folio is large/THP before splitting.  So is_large is used to cache
folio_test_large() result.  Now, we don't need that variable any more
because we don't count retrying and failure of large folios (only counting
that of THP folios).  So, in this patch, is_large is removed to simplify
the code.

This is just code cleanup, no functionality changes are expected.

Link: https://lkml.kernel.org/r/20230510031829.11513-1-ying.huang@intel.com


Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: Xin Hao <xhao@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>