Use drm_gem_object_[handle_]unreference_unlocked where possible

Mostly obvious simplifications.

The i915 pread/pwrite ioctls, intel_overlay_put_image and
nouveau_gem_new were incorrectly using the locked versions
without locking: this is also fixed in this patch.

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/intel_overlay.c

@@ -1179,7 +1179,7 @@ int intel_overlay_put_image(struct drm_device *dev, void *data,
 out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 	mutex_unlock(&dev->mode_config.mutex);
-	drm_gem_object_unreference(new_bo);
+	drm_gem_object_unreference_unlocked(new_bo);
 	kfree(params);
 
 	return ret;