mm/swap: rename lru_pvecs to cpu_fbatches

No change to generated code, but this struct no longer contains any
pagevecs, and not all the folio batches it contains are lru.

Link: https://lkml.kernel.org/r/20220617175020.717127-10-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>