Convert the x86 implementation of AEGIS-128L to use the AEAD SIMD
helpers, rather than hand-rolling the same functionality.  This
simplifies the code and also fixes the bug where the user-provided
aead_request is modified.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>