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: Add SMP support for RISCV

elfloader-tool: explicitly link config libs

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

elfloader: Support multiple RISC-V hart entries

On multi-hart platforms, the bbl will call the payload's entrypoint on
each hart and it is up to the payload to synchronise them for a
deterministic start order. The elfloader only statically allocates one
stack, so we check the hartid before the stack is set.

RISCV: Stop passing hartid and DTB to the seL4 kernel.

elfloader: Force _start on RISC-V to be first

bbl won't load our image correctly if the _start symbol isn't first

elfloader: Remove RISC-V multicore stubs

riscv: fix licenses

- Add missing licenses
- NICTA -> DATA61

RISCV port