crypto: serpent - export common functions for x86_64/i386-sse2 assembler implementations

Serpent SSE2 assembler implementations only provide 4-way/8-way parallel
functions and need setkey and one-block encrypt/decrypt functions.

CC: Dag Arne Osvik <osvik@ii.uib.no>
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@mbnet.fi>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>