video: Add video_is_active function

Add the helper function video_is_active() to test if one video device
is active.

This function can be used in board code to execute operation
only when the display is probed / really used.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>

drivers/video/video-uclass.c

@@ -228,6 +228,20 @@ void video_sync_all(void)
 	}
 }
 
+bool video_is_active(void)
+{
+	struct udevice *dev;
+
+	for (uclass_find_first_device(UCLASS_VIDEO, &dev);
+	     dev;
+	     uclass_find_next_device(&dev)) {
+		if (device_active(dev))
+			return true;
+	}
+
+	return false;
+}
+
 int video_get_xsize(struct udevice *dev)
 {
 	struct video_priv *priv = dev_get_uclass_priv(dev);