drm/xe: Move 'has_flatccs' flag back to platform descriptor

drm/xe: Move 'has_flatccs' flag back to platform descriptor

FlatCCS presence/absence is a flag that should be tracked at the
platform level rather than the IP level.  FlatCCS affects the
device-wide memory initialization and reservations so its effects are
not confined to a single IP block or GT.  This is also a trait that
should be tied to the platform even if the graphics IP itself is not
present (e.g., if we disable the primary GT via configfs).

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20251013200944.2499947-31-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>