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/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 108e4c2..2884b08 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3689,6 +3689,9 @@
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	int ret;
 
+	if (!intel_enable_gtt())
+		return -EIO;
+
 	i915_gem_l3_remap(dev);
 
 	i915_gem_init_swizzling(dev);