Migrate the arm32 NEON implementation of NH into lib/crypto/. This
makes the nh() function be optimized on arm32 kernels.
Note: this temporarily makes the adiantum template not utilize the arm32
optimized NH code. This is resolved in a later commit that converts the
adiantum template to use nh() instead of "nhpoly1305".
Link: https://lore.kernel.org/r/20251211011846.8179-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
