drm/i915: disable 48bit full PPGTT when vGPU is active

Disable 48bit full PPGTT on vGPU too for now.

Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: drm-intel-fixes@lists.freedesktop.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160906040412.1274-3-zhenyuw@linux.intel.com