mkbootimg: Add Loki support

* I want my target-files built images to be Loki'd if the device
  needs Loki.
* With this, devices that rely on Loki can ship Lineage Recovery
  officially.
* Import loki_tool from: https://github.com/Stricted/android_external_loki.

Change-Id: I45ef363e05566268c8f24f7e8939a2d785478fbe
12 files changed