video: Rename CONFIG_DM_VIDEO to CONFIG_VIDEO

Now that all the old code is gone, rename this option. Driver model
migration is now complete.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/nexell_display.c b/drivers/video/nexell_display.c
index 42b8d92..5595796 100644
--- a/drivers/video/nexell_display.c
+++ b/drivers/video/nexell_display.c
@@ -542,7 +542,7 @@
 
 	/*
 	 * set environment variable "fb_addr" (frame buffer address), required
-	 * for splash image, which is not set if CONFIG_DM_VIDEO is enabled).
+	 * for splash image, which is not set if CONFIG_VIDEO is enabled).
 	 */
 	sprintf(addr, "0x%x", dp->fb_addr);
 	debug("%s(): env_set(\"fb_addr\", %s) ...\n", __func__, addr);