* add core-v-mcu bsp

* 规范bsp格式 添加readme

* 修改readme

Co-authored-by: 1516081466@qq.com <ws051000>

* 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

modify：     ../../libcpu/risc-v/e310/stack.c
	rmove unused macro definition
modify：     ../../src/idle.c
	Return to the original version

	save mie into stack
msh  running normaly

modified:   ../../libcpu/risc-v/e310/context_gcc.S
	change  ret to mret and switch to new task with mepc

1. [bsp][sam9260] Fix the bug that auto reset after boot 20s. Disable watchdog in rt_lovel_level_init function.
2. [bsp][sam9260] Modify SCONS scripts to support IAR tool chain.
3. [bsp][sam9260] Move link strips in to folder link_scripts.
4. [libcpu][arm926] Add copy right to source file and format code.

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@1364 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@196 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@4 bbd45198-f89e-11dd-88c7-29a3b14d5316

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2 bbd45198-f89e-11dd-88c7-29a3b14d5316