Improve Serpent key setup speed
* cipher/serpent.c (SBOX, SBOX_INVERSE): Remove index argument. (serpent_subkeys_generate): Use smaller temporary arrays for subkey generation and perform stack clearing locally. (serpent_setkey_internal): Use wipememory to clear stack and remove _gcry_burn_stack. (serpent_setkey): Remove unneeded _gcry_burn_stack.
Avoid using large arrays and large stack burning to gain extra speed for
key setup.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>