tracing: add named event trace

Add support for a "named event" trace. This trace is intentionally not
used by the system. The purpose of this trace is to allow driver or
application developers to quickly add tracing for events for debug
purposes, and to provide an example of how tracing subsystems can be
extended with additional trace identifiers.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>