Currently, this supports SHA1 and SHA2-{224,256,384,512} both as plain
hashes and in HMAC mode on both amd64 and i386. It uses the SHA
intrinsics when present similar to aesni(4), but uses SSE/AVX
instructions when they are not.
Note that some files from OpenSSL that normally wrap the assembly
routines have been adapted to export methods usable by 'struct
auth_xform' as is used by existing software crypto routines.
Reviewed by: gallatin, jkim, delphij, gnn
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D26821
