synquacer: Add MHU driver

Add Message Handling Unit (MHU) driver used to communicate among
Application Processors (AP) and System Control Processor (SCP).

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
diff --git a/plat/socionext/synquacer/drivers/mhu/sq_mhu.h b/plat/socionext/synquacer/drivers/mhu/sq_mhu.h
new file mode 100644
index 0000000..bef117d
--- /dev/null
+++ b/plat/socionext/synquacer/drivers/mhu/sq_mhu.h
@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef __SQ_MHU_H__
+#define __SQ_MHU_H__
+
+#include <stdint.h>
+
+void mhu_secure_message_start(unsigned int slot_id);
+void mhu_secure_message_send(unsigned int slot_id);
+uint32_t mhu_secure_message_wait(void);
+void mhu_secure_message_end(unsigned int slot_id);
+
+void mhu_secure_init(void);
+
+#endif	/* __SQ_MHU_H__ */