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/wandboard_defconfig b/configs/wandboard_defconfig
index 6b49b40..cbf5a5d 100644
--- a/configs/wandboard_defconfig
+++ b/configs/wandboard_defconfig
@@ -75,7 +75,7 @@
 CONFIG_MXC_UART=y
 CONFIG_DM_THERMAL=y
 CONFIG_USB=y
-CONFIG_DM_VIDEO=y
+CONFIG_VIDEO=y
 CONFIG_VIDEO_LOGO=y
 # CONFIG_VIDEO_BPP8 is not set
 # CONFIG_VIDEO_BPP32 is not set