drm/i915: create VLV_DSIPLAY_BASE #define

Will be used more in the next patch.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index ab3b9d3..ff569cc 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1031,7 +1031,7 @@
 	 * This should make it easier to transition modules over to the
 	 * new register block scheme, since we can do it incrementally.
 	 */
-	if (reg >= 0x180000)
+	if (reg >= VLV_DISPLAY_BASE)
 		return false;
 
 	if (reg >= RENDER_RING_BASE &&