[cert] Extract out KeyUsage logic for reuse on the CWT side
[cert] Extract out KeyUsage logic for reuse on the CWT side

Signed-off-by: Miguel Young de la Sota <71b8e7f4945fd97b98544cf897992af89646547a@google.com>

lowRISC/manticore,lowRISC/manticore,lowRISC/manticore