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.

Use appropriate compiler attributes

Clang does not support all of the same attributes as GCC. Need to use
compiler specific attributes

trivial: style this repo

elfloader: fix ARM CPUID message on EFI

At O2 and higher, the switch gets optimised into a table of strings.
Unfortunately, the compiler doesn't properly handle this when building
position-independent code with -fpic - the switch gets turned into this:

404b30: f0000021 adrp x1, 40b000 <cpio_ls+0x4e0>
404b34: 910cc021 add x1, x1, #0x330
404b38: f8605820 ldr x0, [x1, w0, uxtw #3]
404b3c: d65f03c0 ret

which will return the un-relocated address of the string, rather than
the position-independent address. Fix this by forcing the two
affected functions to use O1 even in release builds.

Fix whitespace

- remove trailing whitespace
- remove duplicate blank lines
- remove blank lines at end of file

Fix licenses

elfloader: refactor files to imitate kernel design
- move files to src/include folders
- update files as required, e.g. renaming files and folders to prevent conflicts

Raspberry PI 3 port

Add efi/64bit and Hikey platforms