Copy ctx timestamp at beginning of every GPU job to a saved location.
Used to determine how long a job has been running on the hardware.

v2:
 - - s/ctx_timestamp_job/ctx_job_timestamp
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240611144053.2805091-4-matthew.brost@intel.com