convert license headers to SPDX

Includes license review of 3rd-party files, adding missing upstream
headers, and moving the UNSW OZPLB license into its own file rather
than replicating it in the header.

trivial: style this repo

elfloader: Remove ARM assumption

Rearranges the elfloader to place non ARM specific code into common locations and only
include ARM code if building for ARM. This enables the elfloader to be used for other
architectures in the future.