drm/xe/guc: Cancel ongoing H2G requests when stopping CT

Once we have started a GT reset sequence, which includes stopping
GuC CTB communication, we should also cancel all ongoing H2G send-
recv requests, as either GuC is already dead, or due to imminent
reset GuC will not be able to reply, or due to internal cleanup
we will lose pending fences. With this we will report dedicated
-ECANCELED error instead of misleading -ETIME.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Acked-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250709174038.1876-4-michal.wajdeczko@intel.com