drm/i915: GVT-g driver depends on 64BIT kernel

We currently don't support GVT-g driver on i386 kernel.
Add explicit dependence on 64bit kernel.
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/Kconfig

@@ -86,6 +86,7 @@ config DRM_I915_USERPTR
 config DRM_I915_GVT
         bool "Enable Intel GVT-g graphics virtualization host support"
         depends on DRM_I915
+        depends on 64BIT
         default n
         help
 	  Choose this option if you want to enable Intel GVT-g graphics