trusty: timertest: add stress test mode

Add a long-running stress test that repeatedly sleeps for a short period.  This allows other system aspects to be tested while the Trusty timers are firing.

Bug: 325424592
Test: build.py qemu-generic-arm64-test-debug --test com.android.timer-unittest
Change-Id: I1443db70a671fee9df5dbdf1c9c6d292b83e8817
1 file changed