simpleperf: support reporting more than one event type.
When sampling kernel trace points, it is like to sample more than
one even type. Like `simpleperf record -e kmem:mm_page_alloc,kmem:mm_page_free`.
1. change record command to dump event_id for all records.
2. change report command and record reader to support multiple
3. hide record_cache inside EventSelectionSet.
4. add test to report multiple event types.
17 files changed