treewide: Add SPDX license identifier for missed files

Add SPDX license identifiers to all files which:

 - Have no license information of any form

 - Have EXPORT_.*_SYMBOL_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/arm/xen/enlighten.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <xen/xen.h>
 #include <xen/events.h>
 #include <xen/grant_table.h>

arch/arm/xen/mm.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/cpu.h>
 #include <linux/dma-mapping.h>
 #include <linux/gfp.h>

arch/arm/xen/p2m.c

@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/memblock.h>
 #include <linux/gfp.h>
 #include <linux/export.h>