trusty: timertest: add stress test mode am: 5f0034fa5d

Original change: https://android-review.googlesource.com/c/trusty/app/sample/+/2965048

Change-Id: Ide2ce2b1e8b1ceed272c258ba67fcfec58100b7d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>