drm/xe: Extract non mapped regions out of GuC CTB into its own struct.

No functional change here. The goal is to have a clear split between
the mapped portions of the CTB and the static information, so we can
easily capture snapshots that will be used for later read out with
the devcoredump infrastructure.

Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>