crypto: inside-secure - rework the alg type settings in the context

This patches reworks the way the algorithm type is set in the context,
by using the fact that the decryption algorithms are just a combination
of the algorithm encryption type and CONTEXT_CONTROL_TYPE_NULL_IN.

This will help having simpler code when adding the AEAD support, to
avoid ending up with an endless switch case block.

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