Add script for re-signing final firmware images with the correct keys.

Also add a script for splitting a firmware image into component firmware data, vblocks and the GBB.

Note: The script uses fmap_decode, a utility to parse flashmap of a firmware image, and a part of the flashmap project:

TEST=Tested with newer builds of firmware images with flashmaps enabled. Steps to verify:

1) Use script to re-sign an existing image with a new set of keys.
2) Use to get individual firmware data and vblocks.
3) Use vbutil_firmware with the new keys. Verification should succeed with
   the newer keys but fail with the older ones.

Review URL:
4 files changed