src/signature: print certificate validity times
src/signature: print certificate validity times

This prints the X509 'Not Before'/'Not After' certificate validity
period when the cert chain is dumped.

Signed-off-by: Enrico Joerns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

jluebbe/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc,ejoerns/rauc,rauc/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc