openwrt添加usb storage支持

本例以添加fat和ext文件系統的usb storage爲例，配置openwrt：

kernel_menuconfig:
    Enable the block layer ---> Partition Types ---> PC BIOS (MSDOS partition tables) support
    File systems ---> ext4
    File systems ---> Native language support  ---> Codepage 437
menuconfig:
    Kernel moudles --->  Filesystems --->  kmod-fs-ext4, kmod-fs-vfat
    Kernel moudles ---> USB Support --->  kmod-usb-storage