build: Add script to generate extra images

Change-Id: I53081c7a2b4f18bc8c8a27b04d311a6b078b2022
Use standard qcom naming

Change-Id: I360b3dcf1fe82140a7993189e881f9d77b571bef
[HAX] Allow per-target dtbTool

 * Revert this when fixed

Change-Id: I97ecb0448ae7bd5859454be290c5dde6248b2859
Generate extra userdata partition if needed

* To support variants of devices which may come in 16/32/64GB variants.

Change-Id: I74c32d8316f0450a1445fe95a95e5cabb7a9dd1b