fastboot: add support for v3 boot header format

Support v3 header format when changing the command line with
fastboot boot or using flash:raw.

Bug: 151750405
Test: fastboot boot and flash:raw with updated cmdline and v3 header
Change-Id: Ibf396e2d18d8b22cad50db290f3fd4e46ff85d9b
2 files changed