Replace internal logic with separate bitrev library.

Link: https://lkml.kernel.org/r/20230730081717.1498217-1-sanpeqf@gmail.comSigned-off-by: John Sanpe <sanpeqf@gmail.com>
Cc: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>