drm/i915: call intel_enable_gtt

When drm/i915 is in control of the gtt, we need to call
the enable function at all the relevant places ourselves.

Reviewed-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/include/drm/intel-gtt.h b/include/drm/intel-gtt.h
index 84ebd71..8e29d55 100644
--- a/include/drm/intel-gtt.h
+++ b/include/drm/intel-gtt.h
@@ -27,6 +27,8 @@
 		     struct agp_bridge_data *bridge);
 void intel_gmch_remove(void);
 
+bool intel_enable_gtt(void);
+
 void intel_gtt_chipset_flush(void);
 void intel_gtt_unmap_memory(struct scatterlist *sg_list, int num_sg);
 void intel_gtt_clear_range(unsigned int first_entry, unsigned int num_entries);