drm/xe/guc: Rename xe_guc_register_exec_queue

This function is dedicated for use by the VFs, we shouldn't use
name that might suggests it's general purpose. While there, update
asserts to better reflect intended usage.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Satyanarayana K V P <satyanarayana.k.v.p@intel.com>
Link: https://lore.kernel.org/r/20250908123025.747-2-michal.wajdeczko@intel.com