unpackbootimg: Add support for second, second_offset and tags_offset.

Summary: Change-Id: Ia7ef7f00191dbf2c44736c4e4d980f72afa8c253

Test Plan: Chris see if this help nozomi

Reviewers: synergy, anders3408, jriordan001, raymanfx, donald.munn, rlasalle15

CC: