When a performance monitor is enabled in the context, all the jobs
submitted to the kernel will have attached this monitor ID, so the
kernel will measuring the performance counters selected in the monitor
when these jobs are executed by the GPU (accumulating the results).

v2 (Iago):
 - Update comment
 - Assert fence is not NULL
 - Assert has_perfmon when using perfmon
 - Rewrite conditional
 - Implement performance counters in CSD

v4 (Juan):
 - Track previous perfmon and sync BCL if required (Juan).
 - Track if a job with perfmon was submitted (Juan)

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>