extract_utils: introduce -k (kang mode) option

* The use case is easier updating of pinned blobs. When --kang is set,
  pinning is automatically ignored, and the script will print lines at
  its output that can be directly copied back into the
  proprietary-files.txt.
* Best served together with --section ${SECTION}, and proper grouping
  of the proprietary-files.txt.

Change-Id: I648fbcbd4580a4a002b00828bcfee18d1e265d7b
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>