drm/xe/multi_queue: Refactor CGP_SYNC send path

drm/xe/multi_queue: Refactor CGP_SYNC send path

Factor the repeated CGP_SYNC action build-and-send sequence into a new
helper guc_exec_queue_send_cgp_sync(). Drop the redundant guc parameter
from __register_exec_queue_group() since it can be derived via
exec_queue_to_guc(q). Remove xe_guc_exec_queue_group_add() which is now
identical to the helper and replace its call site directly.

No functional change.

Assisted-by: GitHub Copilot:claude-sonnet-4.6
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260508194428.61819-6-niranjana.vishwanathapura@intel.com