mb/google/kahlee/dsdt.asl: Add method _SWS

_SWS is the recommended method of wake source retrieval. Now that PM1I and
GPEI are available at NVS, add the method _SWS to kahlee/grunt ACPI code.

BUG=b:76020953
TEST=Build grunt

Change-Id: I5930438af40e6f9177462582cafb65401d9c60f4
Signed-off-by: Richard Spiegel <richard.spiegel@silverbackltd.com>
Reviewed-on: https://review.coreboot.org/26217
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/mainboard/google/kahlee/dsdt.asl

@@ -45,6 +45,9 @@ DefinitionBlock (
 	/* Contains the Sleep methods (WAK, PTS, GTS, etc.) */
 	#include <variant/acpi/sleep.asl>
 
+	/* Contains _SWS methods */
+	#include <acpi_wake_source.asl>
+
 	/* System Bus */
 	Scope(\_SB) { /* Start \_SB scope */
 		/* global utility methods expected within the \_SB scope */

src/soc/amd/stoneyridge/acpi/acpi_wake_source.asl

@@ -0,0 +1,32 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2015 Google Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+Scope (\_SB)
+{
+	Method (_SWS)
+	{
+		/* Index into PM1 for device that caused wake */
+		Return (\PM1I)
+	}
+}
+
+Scope (\_GPE)
+{
+	Method (_SWS)
+	{
+		/* Index into GPE for device that caused wake */
+		Return (\GPEI)
+	}
+}