减少sfud对任务栈的占用
减少sfud对任务栈的占用

用全局空间换栈空间，当多个任务需要使用sfud时，可以节省内存
例如多个任务需要使用文件系统，任务栈可以减少
weiyuliang/rt-thread,AubrCool/rt-thread,FlyLu/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,AubrCool/rt-thread,FlyLu/rt-thread,wolfgangz2013/rt-thread,gbcwbz/rt-thread,FlyLu/rt-thread,ArdaFu/rt-thread,RT-Thread/rt-thread,weety/rt-thread,ArdaFu/rt-thread,armink/rt-thread,AubrCool/rt-thread,gbcwbz/rt-thread,wolfgangz2013/rt-thread,weety/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,gbcwbz/rt-thread,nongxiaoming/rt-thread,geniusgogo/rt-thread,hezlog/rt-thread,weiyuliang/rt-thread,weety/rt-thread,weety/rt-thread,geniusgogo/rt-thread,weety/rt-thread,weety/rt-thread,nongxiaoming/rt-thread,weiyuliang/rt-thread,AubrCool/rt-thread,gbcwbz/rt-thread,AubrCool/rt-thread,armink/rt-thread,nongxiaoming/rt-thread,gbcwbz/rt-thread,nongxiaoming/rt-thread,zhaojuntao/rt-thread,wolfgangz2013/rt-thread,RT-Thread/rt-thread,hezlog/rt-thread,FlyLu/rt-thread,FlyLu/rt-thread,hezlog/rt-thread,wolfgangz2013/rt-thread,ArdaFu/rt-thread,geniusgogo/rt-thread,zhaojuntao/rt-thread,FlyLu/rt-thread,nongxiaoming/rt-thread,gbcwbz/rt-thread,zhaojuntao/rt-thread,zhaojuntao/rt-thread,RT-Thread/rt-thread,geniusgogo/rt-thread,weiyuliang/rt-thread,zhaojuntao/rt-thread,hezlog/rt-thread,weety/rt-thread,weiyuliang/rt-thread,gbcwbz/rt-thread,armink/rt-thread,RT-Thread/rt-thread,ArdaFu/rt-thread,ArdaFu/rt-thread,RT-Thread/rt-thread,RT-Thread/rt-thread,nongxiaoming/rt-thread,wolfgangz2013/rt-thread,FlyLu/rt-thread,wolfgangz2013/rt-thread,ArdaFu/rt-thread,armink/rt-thread,armink/rt-thread,zhaojuntao/rt-thread,armink/rt-thread,AubrCool/rt-thread,zhaojuntao/rt-thread,weiyuliang/rt-thread,AubrCool/rt-thread,weiyuliang/rt-thread,nongxiaoming/rt-thread,hezlog/rt-thread,wolfgangz2013/rt-thread,geniusgogo/rt-thread,armink/rt-thread