SHA-512/256 is almost identical to SHA-512, with differing initial
hash values and a truncated output length.

This implementation has been verified using the NIST SHA-512/256 test
vectors.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

SHA-384 is almost identical to SHA-512, with differing initial hash
values and a truncated output length.

This implementation has been verified using the NIST SHA-384 test
vectors.

Signed-off-by: Michael Brown <mcb30@ipxe.org>