drm/xe/vf: Don't try to program MOCS if VF

VFs drivers don't have access to MOCS registers. It is a PF driver
responsibility to program MOCS according to the HW team guidelines.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240405133936.891-3-michal.wajdeczko@intel.com