smptest: Add a check for active cpus. am: e44b33a0ea

Original change: https://android-review.googlesource.com/c/trusty/lk/trusty/+/3503834

Change-Id: Ifd9d6f35ccc86f13e1964110c86ba62fb20a0d82
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>