1, this RomFS's codebase is Nuttx romfs, then it is compatible with
Linux RomFS and you can create such a file system using the tool genromfs.
2, there are two major changes against with the original Nuttx romfs:
    1), it is memory-based: all contents of the fs are stored in the
        memory in the very first stage of "mount".
    2), this version of romfs is altered to be compatible with our new
        version of VFS to take advantage of vnode cache and path cache.

close: #I3S0CP

构建环境的分区文件系统格式不同，会引起du命令计算文件夹size不同，当制作fat格式
的rootfs时，计算的rootfs文件夹的size比fat格式下的小， 则会导致mcopy过程出现
disk full错误。当前通过修正du计算的rootfs文件夹size的方式处理该问题。

close: #I3IA06
Signed-off-by: NYOUR_NAME <zhangfanfan2@huawei.com>
Change-Id: I19c66e35c4382d768e020531a869e1e9186032a7