um: Add SPDX headers for files in arch/um/drivers

Convert files to use SPDX header. All files are licensed under the GPLv2.

Signed-off-by: Alex Dewar <alex.dewar@gmx.co.uk>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/stdio_console.c

@@ -1,6 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0
 /* 
  * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
- * Licensed under the GPL
  */
 
 #include <linux/posix_types.h>