drm/xe: Introduce guc_submit_types.h with relevant structs.

These structs and definitions are only used for the guc_submit
and they were added specifically for the parallel submission.

While doing that also delete the unused struct guc_wq_item.

v2: checkpatch fixes.

Cc: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>