Start converting the LRU from pagevecs to folio_batches.

Combine the functionality of pagevec_add_and_need_flush() with
pagevec_lru_move_fn() in the new folio_batch_add_and_move().

Convert the lru_rotate pagevec to a folio_batch.

Adds 223 bytes total to kernel text, because we're duplicating
infrastructure.  This will be more than made up for in future patches.

Link: https://lkml.kernel.org/r/20220617175020.717127-3-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>