drm/i915: dmesg output for VT-d testing

Our validation guys want to have a positive proof that the gfx driver
is indeed using VT-d, since setting up a gfx stack, especially in
early bring-up and by people not versed in linux gfx is a bit tricky.
So provide just that.

Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1961,6 +1961,10 @@ int i915_gem_gtt_init(struct drm_device *dev)
 		 gtt->base.total >> 20);
 	DRM_DEBUG_DRIVER("GMADR size = %ldM\n", gtt->mappable_end >> 20);
 	DRM_DEBUG_DRIVER("GTT stolen size = %zdM\n", gtt->stolen_size >> 20);
+#ifdef CONFIG_INTEL_IOMMU
+	if (intel_iommu_gfx_mapped)
+		DRM_INFO("VT-d active for gfx access\n");
+#endif
 
 	return 0;
 }