MFC r292782: Replace sys/crypto/sha2/sha2.c with lib/libmd/sha512c.c

cperciva's libmd implementation is 5-30% faster
The same was done for SHA256 previously in r263218

Approved by: secteam

MFC r263219: add sha256c.c to the various modules that included sha2.c...

Catch up with r259980 and handle renamed deflate.c.

Catch up with r259980 and handle renamed deflate.c.