drm/xe/vf: Disable CSC support on VF

CSC is not accessible by VF drivers, so disable its support flag on VF
to prevent further initialization attempts.

Fixes: e02cea83 ("drm/xe/gsc: add Battlemage support")
Signed-off-by: Lukasz Laguna <lukasz.laguna@intel.com>
Cc: Alexander Usyskin <alexander.usyskin@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/r/20250729123437.5933-1-lukasz.laguna@intel.com