Move Bloom filters code into a dedicated section.  Improve the design doc
to explain Bloom filter usage and connection between aging and eviction in
their use.

Link: https://lkml.kernel.org/r/20230118001827.1040870-4-talumbau@google.comSigned-off-by: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>