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/configs/riotboard_defconfig b/configs/riotboard_defconfig
index bd17c02..8ed96c2 100644
--- a/configs/riotboard_defconfig
+++ b/configs/riotboard_defconfig
@@ -73,7 +73,7 @@
 CONFIG_USB=y
 CONFIG_USB_HOST_ETHER=y
 CONFIG_USB_ETHER_ASIX=y
-CONFIG_DM_VIDEO=y
+CONFIG_VIDEO=y
 CONFIG_VIDEO_LOGO=y
 # CONFIG_BACKLIGHT is not set
 # CONFIG_CMD_VIDCONSOLE is not set