[finsh] change comment "Disable the command echo mode or not in default" to "Disable the echo mode in default"

[finsh] add FINSH_ECHO_DISABLE_DEFAULT and remove FINSH_ECHO_MODE_DEFAULT, to control the finsh default echo mode

[finsh] add FINSH_ENABLE_ECHO macro to config the finsh needs echo or not and fix the bsp compile error

re-write for #1138

1. Add macro check in rtdebug.h;
2. Use RT_USING_POSIX for poll/select, stdin etc.
3. Split dfs_posix.h to dfs_posix.h, dfs_poll.h and dfs_select.h;

Use uint8_t/uint32_t etc to replace u_char/u_long etc;
Use getchar for shell input.

    a. 恢复对finsh.h和shell.c的修改；（若需要在Andes AE210P里使用Finsh，请参照bsp/AE210P/readme/readme做修改）

[2] 基于AE210P EVB板；
[3] 详细信息参阅bsp/AE210P/readme文件夹；
    《Andes工程创建和调试》文档；等。