keymaster: Add support to mint and validate tokens

This is the short-term solution for validating and minting tokens using the
keymaster auth token.

Bug: 165843730
Test: auth_token populated with hmac digest
Test: trusty-ut-ctrl -D /dev/trusty-ipc-dev0 \
  com.android.trusty.keymaster.secure.test passes
Change-Id: I53d72f14f97a43d279a1235b5ed28355ccdc6dc3
7 files changed