tracing: Align synth event print fmt

The vast majority of ftrace event print fmt consist of a space-separated
field=value pair. Synthetic event currently use a comma-separated
field=value pair, which sticks out from events created via more
classical means.

Align the format of synth events so they look just like any other event,
for better consistency and less headache when doing crude text-based
data processing.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20250319215028.1680278-1-douglas.raillard@arm.com


Signed-off-by: Douglas Raillard <douglas.raillard@arm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>