Unfortunately, even with a softdep some distros fail to include
the necessary modules in the initrd.  Therefore this patch adds
a fallback path to restore existing behaviour where we cannot
load the new crypto crct10dif algorithm.

In order to do this, the underlying crct10dif has been split out
from the crypto implementation so that it can be used on the
fallback path.
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>