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.

elfloader-tool: explicitly link config libs

explicitly link kernel_autoconf and elfloader_Config
since the global config lib is going to be remove

trivial: fix type aliasing and comment

Fix type aliasing which modern verions of gcc complain about, and
add a comment about SMP stack addresses on the TX1.

elfloader: add AARCH64 SMP booting for HiKey

(1) Add common SMP code for AARCH64.
(2) Add code to activate cores for HiKey (AARCH64 only)