feat(dummy-uart): Add dummy uart

This uart can be used to prevent compiling errors when there is no uart
(currently) supported.

Author: miguelafsilva5

src/platform/drivers/dummy_uart/dummy_uart.c

@@ -0,0 +1,33 @@
+/**
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright (c) Bao Project and Contributors. All rights reserved.
+ */
+
+#include <drivers/dummy_uart.h>
+#include <fences.h>
+
+void uart_init(volatile struct dummy_uart* uart)
+{
+    UNUSED_ARG(uart);
+    return;
+}
+
+void uart_enable(volatile struct dummy_uart* uart)
+{
+    UNUSED_ARG(uart);
+    return;
+}
+
+void uart_putc(volatile struct dummy_uart* uart, int8_t c)
+{
+    UNUSED_ARG(uart);
+    UNUSED_ARG(c);
+    return;
+}
+
+void uart_puts(volatile struct dummy_uart* uart, int8_t const* str)
+{
+    UNUSED_ARG(uart);
+    UNUSED_ARG(str);
+    return;
+}

src/platform/drivers/dummy_uart/inc/drivers/dummy_uart.h

@@ -0,0 +1,23 @@
+/**
+ * SPDX-License-Identifier: Apache-2.0
+ * Copyright (c) Bao Project and Contributors. All rights reserved.
+ */
+
+#ifndef DUMMY_UART_H
+#define DUMMY_UART_H
+
+#include <bao.h>
+// #include <plat/platform.h>
+
+struct dummy_uart {
+    uint32_t dummy_reg; /* 0x0 */
+};
+
+typedef volatile struct dummy_uart bao_uart_t;
+
+void uart_enable(volatile struct dummy_uart* uart);
+void uart_init(volatile struct dummy_uart* uart);
+void uart_puts(volatile struct dummy_uart* uart, const int8_t* str);
+void uart_putc(volatile struct dummy_uart* uart, int8_t str);
+
+#endif /* DUMMY_UART_H */

src/platform/drivers/dummy_uart/objects.mk

@@ -0,0 +1,4 @@
+## SPDX-License-Identifier: Apache-2.0
+## Copyright (c) Bao Project and Contributors. All rights reserved.
+
+drivers-objs-y+=dummy_uart/dummy_uart.o