ata: libata: add qc_prep tracepoint

Convert the existing ata_qc_issue() tracepoint into a template,
and add tracepoints for ata_qc_prep() and ata_qc_issue() based
on that template.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>