lib/crypto: arm64/nh: Migrate optimized code into library

lib/crypto: arm64/nh: Migrate optimized code into library

Migrate the arm64 NEON implementation of NH into lib/crypto/.  This
makes the nh() function be optimized on arm64 kernels.

Note: this temporarily makes the adiantum template not utilize the arm64
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/20251211011846.8179-5-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>