Port Android boot image structures and parsing to Rust

Initial definitions and support for handling Android boot images in
Rust. Contains parallel, ABI compatible definitions for all structs in
bootimg.h as well as parsing helper functions. All parsing functions
are zero-copy.

Test: add unit tests for parsing boot image headers

Change-Id: I4a3f75089075e11231fe91061f320ed34d28dc93
4 files changed