crypto: aegis128/neon - optimize tail block handling

Avoid copying the tail block via a stack buffer if the total size
exceeds a single AEGIS block. In this case, we can use overlapping
loads and stores and NEON permutation instructions instead, which
leads to a modest performance improvement on some cores (< 5%),
and is slightly cleaner. Note that we still need to use a stack
buffer if the entire input is smaller than 16 bytes, given that
we cannot use 16 byte NEON loads and stores safely in this case.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Ondrej Mosnacek <omosnacek@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>