Convert license tags to SPDX identifiers

This commit also converts our own copyright headers to directly use
SPDX, but leaves all other copyright header intact, only adding the
SPDX ident. As far as possible this commit also merges multiple
Data61 copyright statements/headers into one for consistency.

mcs: timeout exceptions

- Add seL4_TCB_SetTimeoutEndpoint
- implement timeout exceptions

Fix licenses (the rest)

s/D61/DATA61/ in license headers for consistency

SELFOUR-413: changes for verification

Avoid using ptrs to arrays at all

Another macrofull change brought to your by verification. This should
avoid nasty proofs about const pointers.