This patch adds support for image unpacking to the FIP packaging
tool. Command line option '-u,--unpack' may be used to unpack the
contents of an existing FIP file into the working directory. The
tool uses default hardcoded filenames for the unpacked images. If
the files already exist, they can be overwritten by specifying the
option '-f,--force'.

Change-Id: I360b11d9c5403e8c0a7a9cac32c1d90ebb228063