backport: crypto: arm64/chacha20 - implement NEON version based on SSE3 code

This is a straight port to arm64/NEON of the x86 SSE3 implementation
of the ChaCha20 stream cipher. It uses the new skcipher walksize
attribute to process the input in strides of 4x the block size.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

backported to 3.10 the same way arm chacha20 SNEON3 imp. for 3.18 was
done : https://android-review.googlesource.com/c/kernel/common/+/551349



Signed-off-by: Mister Oyster <oysterized@gmail.com>