crypto: aegis128 - avoid function pointers for parameterization

Instead of passing around an ops structure with function pointers,
which forces indirect calls to be used, refactor the code slightly
so we can use ordinary function calls. At the same time, switch to
a static key to decide whether or not the SIMD code path may be used.

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