Provide a version of the core AES transform to the aegis128 SIMD
code that does not rely on the special AES instructions, but uses
plain NEON instructions instead. This allows the SIMD version of
the aegis128 driver to be used on arm64 systems that do not
implement those instructions (which are not mandatory in the
architecture), such as the Raspberry Pi 3.

Since GCC makes a mess of this when using the tbl/tbx intrinsics
to perform the sbox substitution, preload the Sbox into v16..v31
in this case and use inline asm to emit the tbl/tbx instructions.
Clang does not support this approach, nor does it require it, since
it does a much better job at code generation, so there we use the
intrinsics as usual.

Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: NNick Desaulniers <ndesaulniers@google.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>