crypto: enforce per-alg crypto key length

crypto: enforce per-alg crypto key length

Crypto algorithms have different requirements on key length. As we do
not support key stretching (eg. PBKDF2), user must provide the exact
key length used by the algorithm.
Failing that means low-level crypto functions might read garbage (eg.
aes128_key_expand() will read 16-bytes, regardless of the key provided
by the user).

Change-Id: I347a1ea7a59720a1ed07ceaad8b00a31f78458c9
Signed-off-by: Benoît Ganne <bganne@cisco.com>