Update register layout in user context

The changes for TLS changed the layout of registers and added registers
for each of the architectures changing the ordering, name, and rules for
initialisation.

trivial: guard with pragma once

SELFOUR-1284: riscv/debug update register names

They now match seL4_UserContext for riscv

riscv: fix licenses

NICTA_BSD -> DATA61_BSD

RISC-V port