Modify the command format of load to "load /dev/fs/filesystem@device/file".
Now the loading command of USB device's FAT filesystem is same as others.
Also, the old format "load /dev/fat/disk@usb0/file" and "load /dev/fat/ram@address/file"
are still supported. Thanks LIU Qi <liuqi82@gmail.com>.
Target: Bonito3a780e