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/common/Kconfig b/common/Kconfig
index 6608a4f..62e7fb5 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -194,7 +194,7 @@
 
 config CONSOLE_MUX
 	bool "Enable console multiplexing"
-	default y if DM_VIDEO || VIDEO || LCD
+	default y if VIDEO || VIDEO || LCD
 	help
 	  This allows multiple devices to be used for each console 'file'.
 	  For example, stdout can be set to go to serial and video.