drm/xe: Store process name and pid in xe file

An xe file can outlive the associated process as the GPU cleanup is just
triggered upon file close (process kill) and completes sometime later.
If the file close triggers error conditions (GPU hangs) the process
cannot be safely referenced to retrieve the name and pid for debug
information. Store the process name and pid directly in the xe file to
be safe.

v2:
 - Access file->pid via rcu_access_pointer (Matthew Auld)

Fixes: b10d0c5e ("drm/xe: Add process name to devcoredump")
Fixes: f6ca930d ("drm/xe: Add process name and PID to job timedout message")
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240723151045.1725417-1-matthew.brost@intel.com