rpi3: Move VC mailbox driver into generic drivers directory

To allow sharing the driver between the RPi3 and RPi4, move the mailbox
driver into the generic driver directory.

Change-Id: I463e49acf82b02bf004f3d56482b7791f3020bc0
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/plat/rpi/rpi3/rpi_mbox_board.c b/plat/rpi/rpi3/rpi_mbox_board.c
new file mode 100644
index 0000000..e7c1e2b
--- /dev/null
+++ b/plat/rpi/rpi3/rpi_mbox_board.c
@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2018-2019, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <assert.h>
+
+#include <platform_def.h>
+
+#include <arch_helpers.h>
+
+#include <drivers/rpi3/mailbox/rpi3_mbox.h>
+
+#define RPI3_MBOX_BUFFER_SIZE		U(256)
+static uint8_t __aligned(16) rpi3_mbox_buffer[RPI3_MBOX_BUFFER_SIZE];
+
+/*******************************************************************************
+ * Request board revision. Returns the revision and 0 on success, -1 on error.
+ ******************************************************************************/
+int rpi3_vc_hardware_get_board_revision(uint32_t *revision)
+{
+	uint32_t tag_request_size = sizeof(uint32_t);
+	rpi3_mbox_request_t *req = (rpi3_mbox_request_t *) rpi3_mbox_buffer;
+
+	assert(revision != NULL);
+
+	VERBOSE("rpi3: mbox: Sending request at %p\n", (void *)req);
+
+	req->size = sizeof(rpi3_mbox_buffer);
+	req->code = RPI3_MBOX_PROCESS_REQUEST;
+
+	req->tags[0] = RPI3_TAG_HARDWARE_GET_BOARD_REVISION;
+	req->tags[1] = tag_request_size; /* Space available for the response */
+	req->tags[2] = RPI3_TAG_REQUEST;
+	req->tags[3] = 0; /* Placeholder for the response */
+
+	req->tags[4] = RPI3_TAG_END;
+
+	rpi3_vc_mailbox_request_send(req, RPI3_MBOX_BUFFER_SIZE);
+
+	if (req->code != RPI3_MBOX_REQUEST_SUCCESSFUL) {
+		ERROR("rpi3: mbox: Code = 0x%08x\n", req->code);
+		return -1;
+	}
+
+	if (req->tags[2] != (RPI3_TAG_IS_RESPONSE | tag_request_size)) {
+		ERROR("rpi3: mbox: get board revision failed (0x%08x)\n",
+		      req->tags[2]);
+		return -1;
+	}
+
+	*revision = req->tags[3];
+
+	return 0;
+}