drm/xe/vf: Skip engine ring enabling if VF

All engines will be correctly initialized by the PF driver.
Moreover, VF drivers can't access related engine registers.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240619214557.905-9-michal.wajdeczko@intel.com