mm/swap: remove boilerplate

mm/swap: remove boilerplate

Remove boilerplate by using a macro to choose the corresponding lock and
handler for each folio_batch in cpu_fbatches.

[yuzhao@google.com: handle zero-length local_lock_t]
Link: https://lkml.kernel.org/r/Zq_0X04WsqgUnz30@google.com
[yuzhao@google.com: fix "BUG: using smp_processor_id() in preemptible"]
Link: https://lkml.kernel.org/r/ZqNHHMiHn-9vy_II@google.com
Link: https://lkml.kernel.org/r/20240711021317.596178-6-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Hugh Dickins <hughd@google.com>
Cc: Barry Song <21cnbao@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>