drm/xe: Stop accumulating LRC timestamp on job_free

drm/xe: Stop accumulating LRC timestamp on job_free

The exec queue timestamp is only really useful when it's being queried
through the fdinfo. There's no need to update it so often, on every
job_free. Tracing a simple app like vkcube running shows an update
rate of ~ 120Hz. In case of discrete, the BO is on vram, creating a lot
of pcie transactions.

The update on job_free() is used to cover a gap: if exec
queue is created and destroyed rapidly, before a new query, the
timestamp still needs to be accumulated and accounted for in the xef.

Initial implementation in commit 6109f24f87d7 ("drm/xe: Add helper to
accumulate exec queue runtime") couldn't do it on the exec_queue_fini
since the xef could be gone at that point. However since commit
ce8c161cbad4 ("drm/xe: Add ref counting for xe_file") the xef is
refcounted and the exec queue always holds a reference, making this safe
now.

Improve the fix in commit 2149ded63079 ("drm/xe: Fix use after free when
client stats are captured") by reducing the frequency in which the
update is needed.

Fixes: 2149ded63079 ("drm/xe: Fix use after free when client stats are captured")
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241104143815.2112272-3-lucas.demarchi@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>