drm/i915: optimize vblank waits in set_base_atomic

We only need to do them if the pipe is actually running and if the
framebuffers have changed. Removes two "wait for vblank timed out"
messages when doing a suspend/resume cycle on my i855gm.

v2: s/to_intel_ctrc(crtc)/intel_crtc/ spotted by Chris.
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2212,7 +2212,8 @@ intel_pipe_set_base(struct drm_crtc *crtc, int x, int y,
 	crtc->y = y;
 
 	if (old_fb) {
-		intel_wait_for_vblank(dev, intel_crtc->pipe);
+		if (intel_crtc->active && old_fb != fb)
+			intel_wait_for_vblank(dev, intel_crtc->pipe);
 		intel_unpin_fb_obj(to_intel_framebuffer(old_fb)->obj);
 	}