Make tracepoint probe support listing mode -L

Make tracepoint probe support listing mode -L

This patch is to enable displaying arguments of tracepoint
probe in listing mode -L. The example output is like

$stap -L 'kernel.trace("block_bio*")'
kernel.trace("block_bio_bounce") $q:struct request_queue* $bio:struct bio*
kernel.trace("block_bio_backmerge") $q:struct request_queue* $bio:struct bio*
kernel.trace("block_bio_complete") $q:struct request_queue* $bio:struct bio*
kernel.trace("block_bio_queue") $q:struct request_queue* $bio:struct bio*
kernel.trace("block_bio_frontmerge") $q:struct request_queue* $bio:struct bio*

Signed-off-by: Wenji Huang <wenji.huang@oracle.com>