romfs : Add two field, length of file name and file name, in romfs_get_file_by_hash. Add function to show file name.
[NEW FORMAT]

|    hash    |   LFN    | file name | length of a file | file content  |
|   4 bytes  | 1 byte   |   m bytes |   4 bytes        |    n bytes    |

LFN: Length of File Name

reterence: AdrianHuang