perf cs-etm: Split setup and timestamp search functions

This refactoring has some benefits:
 * Decoding is done to find the timestamp. If we want to print errors
   when maps aren't available, then doing it from cs_etm__setup_queue()
   may cause warnings to be printed.
 * The cs_etm__setup_queue() flow is shared between timed and timeless
   modes, so it needs to be guarded by an if statement which can now
   be removed.
 * Allows moving the setup queues function earlier.
 * If data was piped in, then not all queues would be filled so it
   wouldn't have worked properly anyway. Now it waits for flush so
   data in all queues will be available.

The motivation for this is to decouple setup functions with ones that
involve decoding. That way we can move the setup function earlier when
the formatted/unformatted trace information is available.

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: James Clark <james.clark@arm.com>