ARM / highbank: add support for pl320 IPC

The pl320 IPC allows for interprocessor communication between the
highbank A9 and the EnergyCore Management Engine. The pl320 implements
a straightforward mailbox protocol.

Signed-off-by: Mark Langsdorf <mark.langsdorf@calxeda.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/include/linux/mailbox.h b/include/linux/mailbox.h
new file mode 100644
index 0000000..5161f63
--- /dev/null
+++ b/include/linux/mailbox.h
@@ -0,0 +1,17 @@
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope 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.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+int pl320_ipc_transmit(u32 *data);
+int pl320_ipc_register_notifier(struct notifier_block *nb);
+int pl320_ipc_unregister_notifier(struct notifier_block *nb);