* [libcpu][riscv]移除ch32中的冗余文件,使用common下的文件

* 修正cpuport.h宏定义

* 规范宏定义格式

* [rtdef] rename RT_WEAK attribute as rt_weak

* [rtdef] rename RT_USED attribute as rt_used

* [rtdef] rename RT_SECTION attribute as rt_section

* [rtdef] rename ALIGN attribute as rt_align

* [legacy] add RT_USED ALIGN RT_SECTION RT_WEAK as legacy support

* 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: NRbb666 <zhangbingru@rt-thread.com>
Co-authored-by: Nzhkag <zhkag@foxmail.com>

WCH CH569W-R0-1v0 evt board bsp port, first version

dev/test under Ubuntu 20.04
toolchain from MounRiver_Studio_Community_Linux_x64_V120

tested drivers : SysTick, gpio, gpio interrupt, uart1 (RX interrupt, TX polling)

libcpu/risc-v/SConscript :
group includes rtconfig.CPU only if folder exists

libcpu/risc-v/common/cpuport.c/rt_hw_context_switch_interrupt() :
make it RT_WEAK for customization