Migrate the x86_64 implementations of NH into lib/crypto/. This makes
the nh() function be optimized on x86_64 kernels.
Note: this temporarily makes the adiantum template not utilize the
x86_64 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/20251211011846.8179-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
a229d83235