spdx: Modify spdx tag from GPL-2.0 to GPL-2.0-only

Modify spdx tag for all CAF authored files for Kona.

Change-Id: I9308c7189412b1e428a7f67ded0dc076b0e38254
Signed-off-by: Rishabh Bhatnagar <rishabhb@codeaurora.org>
diff --git a/mm/showmem.c b/mm/showmem.c
index 62bea47..aa74c71 100644
--- a/mm/showmem.c
+++ b/mm/showmem.c
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (c) 2018, The Linux Foundation. All rights reserved.
  */