coresight: etm4x: docs: Update ABI doc for new sysfs name scheme.

Recent updates to CoreSight drivers have changed the component naming
schema used in sysfs.

This updates the ABI document to reflect the new naming schema.

Signed-off-by: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>