lib/utils: Add RPMI messaging protocol and shared memory transport support

The RISC-V Platform Management Interface (RPMI) defines a messaging protocol
and shared memory based transport for bi-directional communication with an
on-chip or external microcontroller.

To support RPMI in OpenSBI, add:
1) The RPMI messaging protocol defines and helper macros
2) A FDT mailbox driver for the RPMI shared memory transport

Signed-off-by: Rahul Pathak <rpathak@ventanamicro.com>
Co-developed-by: Subrahmanya Lingappa <slingappa@ventanamicro.com>
Signed-off-by: Subrahmanya Lingappa <slingappa@ventanamicro.com>
Co-developed-by: Anup Patel <apatel@ventanamicro.com>
Signed-off-by: Anup Patel <apatel@ventanamicro.com>

include/sbi_utils/mailbox/rpmi_mailbox.h

@@ -0,0 +1,32 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2023 Ventana Micro Systems Inc.
+ *
+ * Authors:
+ *   Anup Patel <apatel@ventanamicro.com>
+ */
+
+#ifndef __RPMI_MAILBOX_H__
+#define __RPMI_MAILBOX_H__
+
+#include <sbi/sbi_error.h>
+#include <sbi_utils/mailbox/rpmi_msgprot.h>
+
+#define rpmi_u32_count(__var)	(sizeof(__var) / sizeof(u32))
+
+/** Convert RPMI error to SBI error */
+int rpmi_xlate_error(enum rpmi_error error);
+
+/** Typical RPMI normal request with at least status code in response */
+int rpmi_normal_request_with_status(
+			struct mbox_chan *chan, u32 service_id,
+			void *req, u32 req_words, u32 req_endian_words,
+			void *resp, u32 resp_words, u32 resp_endian_words);
+
+/* RPMI posted request which is without any response*/
+int rpmi_posted_request(
+		struct mbox_chan *chan, u32 service_id,
+		void *req, u32 req_words, u32 req_endian_words);
+
+#endif /* !__RPMI_MAILBOX_H__ */