SHA-224 is almost identical to SHA-256, with differing initial hash
values and a truncated output length.
This implementation has been verified using the NIST SHA-224 test
vectors.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
Update the digest self-tests to use okx(), and centralise concepts and
data shared between tests for multiple algorithms to reduce duplicated
code.
Signed-off-by: Michael Brown <mcb30@ipxe.org>