drm/xe/kunit: Allow to replace xe_guc_ct_send_recv() with stub

We want to use replacement functions in upcoming kunit tests.

Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://lore.kernel.org/r/20240104222031.277-9-michal.wajdeczko@intel.com
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>