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: update manual

Major manual update with details of the MCS configuration option of the
kernel.

manual: Correct CNode slot size in bytes

It is 16 bytes on 32-bit systems and 32 bytes on 64-bit systems

SELFOUR-6: Add GrantReply to the rights system.

GrantReply is a new access right added to endpoint capabilities, which
allows seL4_Call to be used on those capabilities (specifically, it
allows reply caps *only* to be granted across endpoints).

Prior to the addition of GrantReply, endpoint capabilities required the
Grant access right, which allowed any arbitrary capabilitiy to be
transferred over an endpoint. Using GrantReply, systems can now be
constructed where threads using seL4_Call over an endpoint do not need to be in the same
security subsystem.

manual: Minor fixes, notably last vestige of recycling

SELFOUR-413: refactor libsel4 fault API

This is a *breaking API change*

This commit:

* makes seL4_Fault_tag_t common between the kernel and libsel4
* deprecates the existing functions from sel4/messages.h includes
* introduces a new fault API in sel4/faults.h and
* sel4/sel4_arch/faults.h
* deprecates seL4_GetTag(), as the function did not work without
the user calling seL4_SetTag() first (seL4_MessageInfo is passed
in registers and not set in the IPC buffer)
* removes previously deprecated functions (deprecated prior to 3.0.0)
* updates the seL4 manual to reflect the changes

manual: Split up UntypedRetype documentation

The API documentation for UntypedRetype went into great detail about
kernel object sizes and treatment of capabilities. This change moves
these parts of UntypedRetype's documentation into the relevant sections
of the manual.

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

manual: Corrected introduction of cnode radix

manual: Reword some cspace explanation for clarity

SELFOUR-279: rename Wait -> Recv, add wrappers for seL4_Poll and seL4_Wait for notification objects.

This commit deprecates seL4_ReplyWait, removes seL4_NBwait completely,
and changes the return type of seL4_Wait to void (seL4_Wait should be
used for notification objects, and seL4_Recv should be used where
seL4_Wait was used previously for endpoints).

manual: notification/signalling terminology

Terminology clarification:
- synchronous endpoints -> endpoints
- asynchronous endpoints -> notifications (and notification objects)
- notify -> signal

Also minor language edits.

Revert "s/AEP/Notification/ completed commit :-("

Committed to wrong branch

This reverts commit 50810ac44a4f90f07cfe1aba6f8bf14c30f1d85d.

s/AEP/Notification/ completed commit :-(

Had forgotten the "-a", bear with me, I'm a git newbie...

manual: Purely cosmetic changes / improved wording

Release snapshot