mb/clevo: Rename l140cu to cml-u

In addition to CB:45664, rename clevo/l140cu to clevo/cml-u being able
to add more variants under a generic mainboard later.

Change-Id: I9c16e24830ebb80752df302aa2e63d9df8edad95
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/45665
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/clevo/cml-u/Kconfig

@@ -23,7 +23,7 @@ config BOARD_SPECIFIC_OPTIONS
 
 config MAINBOARD_DIR
 	string
-	default "clevo/l140cu"
+	default "clevo/cml-u"
 
 config MAINBOARD_PART_NUMBER
 	string