crypto: twofish: Rename twofish to twofish_generic and add an alias

This fixes the broken autoloading of the corresponding twofish assembler
ciphers on x86 and x86_64 if they are available. The module name of the
generic implementation was in conflict with the alias in the assembler
modules. The generic twofish c implementation is renamed to
twofish_generic according to the other algorithms with assembler
implementations and an module alias is added for 'twofish'. You can now
load 'twofish' giving you the best implementation by priority,
'twofish-generic' to get the c implementation or 'twofish-asm' to get
the assembler version of cipher.

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