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;

1. Add poll/select APIs;
2. Add wait queue implementation;
3. Remove DFS_STATUS_* code and use errno;
4. Add pipe API;
5. Use a standalone fops in DFS;

[DFS] To make sure the "console" device exist or not when initialize
console device.

修正components.h中使能RT_USING_DFS_RAMFS宏时，加入ramfs.h头文件

比如实际目录为abcde，msh执行 cd abc也能执行成功，判断名称时存在bug

Signed-off-by: pangwei <271372443@qq.com>

To avoid same file name, therefore change the netdb.c to lwip_netdbc in
dfs_lwip.

System will crash when the romfs is erased. Add checks before using them
to avoid it.