crypto: inside-secure - make the key and context size computation dynamic

This patches makes the key and context size computation dynamic when
using memzero_explicit() on these two arrays. This is safer, cleaner and
will help future modifications of the driver when these two parameters
sizes will changes (the context size will be bigger when using AEAD
algorithms).

Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>