* 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>
If the application defines dozens of global variables,
the speed of clearing the bss segment will be slower.
Because icache can be enabled before the mmu enabled.
Therefore, in order to speed up the process of clearing the BSS segment,
enable icache needs to be put ahead.
