trace: implement registration payload

trace: implement registration payload

The trace function payloads such as rte_trace_point_emit_* have
dual functions. The first to emit the payload for the registration
function and the second one to act as trace memory emitters.

When it is used as registration payload, it will do the following to
fulfill the registration job.
- Find out the size of the event,
- Generate metadata field string using __rte_trace_point_emit_field().

Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Signed-off-by: Sunil Kumar Kori <skori@marvell.com>
Acked-by: David Marchand <david.marchand@redhat.com>