mm: multi-gen LRU: use macro for bitmap

Use DECLARE_BITMAP macro when possible.

Link: https://lkml.kernel.org/r/20230522112058.2965866-1-talumbau@google.com
Signed-off-by: T.J. Alumbaugh <talumbau@google.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Yuanchu Xie <yuanchu@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>