drm/xe/guc: Add kernel-doc for xe_guc_ct_send_recv()

Add initial documentation for recently updated xe_guc_ct_send_recv().

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240112102554.761-2-michal.wajdeczko@intel.com