drm/xe: Always write GEN12_RCU_MODE.GEN12_RCU_MODE_CCS_ENABLE for CCS engines

If CCS0 was fused we did not write this register thus CCS engine were
not enabled resulting in driver load failures.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>