Implement Secretkeeper bootloader client library am: 97f9dc99fe am: 462baaf2ed

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

Change-Id: Ibff2078775dae76fb03912d2e58ce7fc975f7933
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>