utils/trace_cmd: reduce regex use
utils/trace_cmd: reduce regex use

Do not attempt to regex match each line for dropped events/preamble. Use
substring search to detect them first, and only use regex on relevant
lines.

jimboatarm/workload-automation,jimboatarm/workload-automation,bjackman/workload-automation,bjackman/workload-automation,jimboatarm/workload-automation,bjackman/workload-automation,jimboatarm/workload-automation,bjackman/workload-automation,jimboatarm/workload-automation,bjackman/workload-automation,jimboatarm/workload-automation,bjackman/workload-automation