crypto: inside-secure - rework cipher functions for future AEAD support

This patch reworks the Inside Secure cipher functions, to remove all
skcipher specific information and structure from all functions generic
enough to be shared between skcipher and aead algorithms.

This is a cosmetic only patch.
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>