Use Trusty secure storage

The number of stored secrets is expected to be small, so use a simple
one-file-per-secret approach to storing the secret in secure storage.

Use a "v1_" prefix for the filenames to make this easier to change in
future, if the expected number of secrets changes.

Test: VtsSecretkeeperTargetTest (including delete_all test)
Bug: 306364873
Change-Id: Ib1d2a0f8aaa27939ec33263d300f17fe835a2a26
3 files changed