remap(), folio_ref_unfreeze(), lru_add_split_folio() are not relevant to
splitting unmapped folio operations. Move them out to the caller so that
__split_unmapped_folio() only handles unmapped folio splits. This makes
__split_unmapped_folio() reusable.
Convert VM_BUG_ON(mapping) to use VM_WARN_ON_ONCE_FOLIO().
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Acked-by: Balbir Singh <balbirs@xxxxxxxxxx>
---