Add DDR refresh config to pei data structure.

Allow platform customized DDR config, including forcing refresh rate to
2x.

Change-Id: I311ae7ddf25142153c94a3fc3fb0a36e03f50ab2
Reviewed-on: https://gerrit.chromium.org/gerrit/50476
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>
Tested-by: Shawn Nematbakhsh <shawnn@chromium.org>
Commit-Queue: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-on: http://review.coreboot.org/4213
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/northbridge/intel/sandybridge/pei_data.h

@@ -121,6 +121,14 @@ struct pei_data
 	 * 2 2N
 	 */
 	int nmode;
+	/* DDR refresh rate config. JEDEC Standard No.21-C Annex K allows
+	 * for DIMM SPD data to specify whether double-rate is required for
+	 * extended operating temperature range.
+	 * 0 Enable double rate based upon temperature thresholds
+	 * 1 Normal rate
+	 * 2 Always enable double rate
+	 */
+	int ddr_refresh_rate_config;
 } __attribute__((packed));
 
 #endif