trusty/storage: Add property indicating when fs is ready am: 4762c22aba

Original change: https://googleplex-android-review.googlesource.com/c/platform/system/core/+/20600926

Change-Id: Id8336bef53d7523d97c8f2c7d137b18946ec63e2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>