cert_tool: update for compatibility with OpenSSL v1.1

This patch fixes incompatibility issues that prevent building the cert_tool
with OpenSSL >= v1.1.0. The changes introduced are still backwards
compatible with OpenSSL v1.0.2.

Fixes arm-software/trusted-fw#521

Signed-off-by: Michalis Pappas <mpappas@fastmail.fm>
4 files changed