drm/i915/guc: Update debugfs for GuC multi-lrc

Display the workqueue status in debugfs for GuC contexts that are in
parent-child relationship.

v2:
 (John Harrison)
  - Output number children in debugfs

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211014172005.27155-16-matthew.brost@intel.com