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.
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.
Changes finaliseCap to return a generic definition of cleanup information that
needs to be done, instead of just encoding an IRQ number. The post deletion information
is encoded as a `cap_t` due to the capability type already being a union of all
the possible information. Aside from providing a properly generic mechanism the motivation
is to support a similar cleanup phase for I/O ports in the future.
