sync branch rt-smart. (#6641)

* Synchronize the code of the rt mart branch to the master branch.
  * TTY device
  * Add lwP code from rt-smart
  * Add vnode in DFS, but DFS will be re-write for rt-smart
  * There are three libcpu for rt-smart:
    * arm/cortex-a, arm/aarch64
    * riscv64

Co-authored-by: Rbb666 <zhangbingru@rt-thread.com>
Co-authored-by: zhkag <zhkag@foxmail.com>

libcpu/mips/gs264/cpuport.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (c) 2006-2020, RT-Thread Development Team
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Change Logs:
+ * Date           Author       Notes
+ */
+
+#ifndef  CPUPORT_H__
+#define  CPUPORT_H__
+
+#ifdef RT_USING_SMP
+typedef union {
+    unsigned long slock;
+    struct __arch_tickets {
+        unsigned short owner;
+        unsigned short next;
+    } tickets;
+} rt_hw_spinlock_t;
+#endif
+
+#endif  /*CPUPORT_H__*/