These queries are used to retrieve the different hardware counters
values, useful to detect performance issues.

v2 (Iago):
 - Fix copyright
 - Assert hwperfmon exists
 - Print message on error
 - Rename hwperfmon structure to make it clear

v4 (Juan):
 - Save last_job_fence when perfmon is stopped

v5 (Juan):
 - No need to ask for counter values if no job was submitted

v6 (Juan):
 - Ensure to flush all jobs before capturing last job fence

v7 (Iago)
 - No braces for single-line body conditionals

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Part-of: <!10666>