doc: update revent documentation
doc: update revent documentation

Forward-port the updated revent documentation from WA2, including
recording format description.

ARM-software/workload-automation,setrofim/workload-automation,ARM-software/workload-automation,setrofim/workload-automation,lisatn/workload-automation,lisatn/workload-automation,ARM-software/workload-automation,lisatn/workload-automation,setrofim/workload-automation,lisatn/workload-automation,ARM-software/workload-automation,setrofim/workload-automation