drm: move drm vblank initialization/cleanup to driver load/unload

drm vblank initialization keeps track of the changes in driver-supplied
frame counts across vt switch and mode setting, but only if you let it by
not tearing down the drm vblank structure.

Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/i915_dma.c

@@ -856,6 +856,13 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 
 	spin_lock_init(&dev_priv->user_irq_lock);
 
+	ret = drm_vblank_init(dev, I915_NUM_PIPE);
+
+	if (ret) {
+		(void) i915_driver_unload(dev);
+		return ret;
+	}
+
 	return ret;
 }