replacing all ifndef with pargma once

All the kernel header files now use pargma once rather than the ifndef,
as the pre-processed C files do not change while header files
are protected with pargma once. This will also solve any naming issues
caused by ifndef.

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: scheduling context donation over ipc

After this commit, threads blocked on an endpoint can recieve a
scheduling context from the thread that wakes the blocked thread.

style: consistently align pointer with name

Run astyle with align-pointer=name

Remove recycle

Removes the recycle operation and adds an operation
to cancel any badged sends on and endpoint. Calling
Revoke + CancelBadgedSend is equivalent to Recycle
on a badged endpoint

SELFOUR-114: remove duplication of seL4_MessageInfo_t, adjust naming to avoid cparser mangling

unsigned int -> word_t

Release snapshot