[CRYPTO] twofish: Split out common c code

This patch splits up the twofish crypto routine into a common part ( key
setup  ) which will be uses by all twofish crypto modules ( generic-c , i586
assembler and x86_64 assembler ) and generic-c part. It also creates a new
header file which will be used by all 3 modules.

This eliminates all code duplication.

Correctness was verified with the tcrypt module and automated test scripts.

Signed-off-by: Joachim Fritschi <jfritschi@freenet.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>