crypto: sha256 - Expose SHA256 generic routine to be callable externa… …lly. 2

Other SHA256 routine may need to use the generic routine when
FPU is not available.

Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>

https://github.com/neobuddy89/hammerhead/commit/dc9dd31f9fd422b27c92b840d82ac68af645dbae