treewide: Add SPDX license identifier for more missed files

Add SPDX license identifiers to all files which:

 - Have no license information of any form

 - Have MODULE_LICENCE("GPL*") inside which was used in the initial
   scan/conversion to ignore the file

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/mm/debug_pagetables.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/debugfs.h>
 #include <linux/efi.h>
 #include <linux/module.h>