unpackbootimg: add a target specifically for unpackbootimg

Change-Id: I8c71a56505d155f43d0776074c09404ce6f6d34b
build: Add unpackbootimg to dist_tools

Change-Id: I58622b8f0a85db18fabdc2cf96d11c5982a9c9d8
Merge "unpackbootimg: add a target specifically for unpackbootimg" into android-4.4
Merge "build: Add unpackbootimg to dist_tools" into android-4.4
Merge branch 'android-4.4' of https://github.com/omnirom/android_build into android-4.4