cr50: add reset extension command

While USB updates have a mechanism to trigger the target reset, SPI
updates do not have it.

This patch adds an extension command to cause the device reset.

BRANCH=none
BUG=chrome-os-partner:58226
TEST=with the rest of the patches applied verified that the system
     gets reset and the new image version kicks in on both gru (over
     SPI) and reef (over USB).

Change-Id: I498538670e2c43d17b13510288eb9ae75eb7b761
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/395628
Reviewed-by: Bill Richardson <wfrichar@chromium.org>

board/cr50/build.mk

@@ -42,6 +42,7 @@ board-y += tpm2/hash_data.o
 board-y += tpm2/hkdf.o
 board-y += tpm2/manufacture.o
 board-y += tpm2/platform.o
+board-y += tpm2/post_reset.o
 board-y += tpm2/rsa.o
 board-y += tpm2/stubs.o
 board-y += tpm2/trng.o

board/cr50/tpm2/post_reset.c

@@ -0,0 +1,20 @@
+/* Copyright 2016 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#include "config.h"
+#include "board.h"
+#include "extension.h"
+
+void post_reset_command_handler(void *body,
+				size_t cmd_size,
+				size_t *response_size)
+{
+	*response_size = 1;
+	((uint8_t *)body)[0] = 0;
+	post_reboot_request();
+}
+
+DECLARE_EXTENSION_COMMAND(EXTENSION_POST_RESET, post_reset_command_handler);

include/extension.h

@@ -53,6 +53,7 @@ enum {
 	EXTENSION_FW_UPGRADE = 4,
 	EXTENSION_HKDF = 5,
 	EXTENSION_ECIES = 6,
+	EXTENSION_POST_RESET = 7,
 };