chromeos: Implement locating and decoding wifi sar data from VPD

A VPD entry "wifi_sar" needs to be created which contains a heximal
encoded string in length of 40 bytes. get_wifi_sar_limits() function
retrieves and decodes the data from the VPD entry, which would later
be consumed by platform code.

BUG=chrome-os-partner:60821
TEST=Build and boot lars and reef

Change-Id: I923b58a63dc1f8a7fdd685cf1c618b2fdf4e7061
Signed-off-by: Robbie Zhang <robbie.zhang@intel.com>
Reviewed-on: https://review.coreboot.org/17958
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/sar.h

@@ -0,0 +1,38 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2017 Intel Corp.
+ *
+ * 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.
+ */
+#ifndef _SAR_H_
+#define _SAR_H_
+
+#include <stdint.h>
+
+#define NUM_SAR_LIMITS 4
+#define BYTES_PER_SAR_LIMIT 10
+
+/* Wifi SAR limit table structure */
+struct wifi_sar_limits {
+	/* Total 4 SAR limit sets, each has 10 bytes */
+	uint8_t sar_limit[NUM_SAR_LIMITS][BYTES_PER_SAR_LIMIT];
+};
+
+/*
+ * Retrieve the SAR limits data from VPD and decode it.
+ * sar_limits:	Pointer to wifi_sar_limits where the resulted data is stored
+ *
+ * Returns:	0 on success, -1 on errors (The VPD entry doesn't exist, or the
+ * VPD entry contains non-heximal value.)
+ */
+int get_wifi_sar_limits(struct wifi_sar_limits *sar_limits);
+
+#endif /* _SAR_H_ */