Support for NXP's i.MX8 SoCs IPC

NXP's i.MX8 SoCs have system controller (M4 core)
which takes control of clock management, power management,
partition management, PAD management etc., other
clusters like Cortex-A35 can send out command via MU
(Message Unit) to system controller for clock/power
management etc..

This patch adds basic IPC(inter-processor communication) support.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
diff --git a/plat/imx/common/include/sci/sci_ipc.h b/plat/imx/common/include/sci/sci_ipc.h
new file mode 100644
index 0000000..c169a79
--- /dev/null
+++ b/plat/imx/common/include/sci/sci_ipc.h
@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+/*!
+ * Header file for the IPC implementation.
+ */
+
+#ifndef SC_IPC_H
+#define SC_IPC_H
+
+/* Includes */
+
+#include <sci/sci_types.h>
+
+/* Defines */
+
+/* Types */
+
+/* Functions */
+
+/*!
+ * This function opens an IPC channel.
+ *
+ * @param[out]    ipc         return pointer for ipc handle
+ * @param[in]     id          id of channel to open
+ *
+ * @return Returns an error code (SC_ERR_NONE = success, SC_ERR_IPC
+ *         otherwise).
+ *
+ * The \a id parameter is implementation specific. Could be an MU
+ * address, pointer to a driver path, channel index, etc.
+ */
+sc_err_t sc_ipc_open(sc_ipc_t *ipc, sc_ipc_id_t id);
+
+/*!
+ * This function closes an IPC channel.
+ *
+ * @param[in]     ipc         id of channel to close
+ */
+void sc_ipc_close(sc_ipc_t ipc);
+
+/*!
+ * This function reads a message from an IPC channel.
+ *
+ * @param[in]     ipc         id of channel read from
+ * @param[out]    data        pointer to message buffer to read
+ *
+ * This function will block if no message is available to be read.
+ */
+void sc_ipc_read(sc_ipc_t ipc, void *data);
+
+/*!
+ * This function writes a message to an IPC channel.
+ *
+ * @param[in]     ipc         id of channel to write to
+ * @param[in]     data        pointer to message buffer to write
+ *
+ * This function will block if the outgoing buffer is full.
+ */
+void sc_ipc_write(sc_ipc_t ipc, void *data);
+
+sc_ipc_t ipc_handle;
+
+#endif				/* SC_IPC_H */