drm/xe: Don't check BIOS-disabled FlatCCS if primary GT is disabled

drm/xe: Don't check BIOS-disabled FlatCCS if primary GT is disabled

If the primary is GT is disabled via configfs, we can't read the GT
registers that would tell us whether the BIOS has disabled FlatCCS on a
platform that would otherwise have it; we'll just proceed as if the
FlatCCS is still enabled.  This is similar to the situation seen by
SRIOV VFs and doesn't cause any functional problems since the hardware
will simply drop writes to the CCS region and reads will always come
back as 0 (indicating uncompressed data).  We'll simply miss out on the
chance to avoid some unnecessary overhead during BO creation and
migration.

Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20251013200944.2499947-45-matthew.d.roper@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>