Implement Secretkeeper bootloader client library am: 97f9dc99fe

Original change: https://android-review.googlesource.com/c/trusty/external/trusty/+/2919725

Change-Id: Ied7b26a3fe6243ee0d7412e8982903ac155ca24f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>