FROMLIST: tracing: add trace_export support for event trace

Only function traces can be exported to other destinations currently.
This patch exports event trace as well. Move trace export related
function to the beginning of file so other trace can call
trace_process_export() to export.

Bug: 160464759
Link: https://lore.kernel.org/patchwork/cover/1280618/


Signed-off-by: Tingwei Zhang <tingwei@codeaurora.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Change-Id: I140476398b889c0c793a4be972437012d2ad9552