Read Verified Boot key from system property in default KeyMint implementation. am: c1bf5f8a6d

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/3360186

Change-Id: I85770b5f2f9f3768473179ed82011b91b7ec03b4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>