Merge branch '2023-08-31-replace-more-init-hooks-with-events' into next

To quote the author:
This series replaces some more of the init hooks in board_f.c and
board_r.c with events. Notably it converts last_state_init() over.

It also provides a 'simple' event spy, which takes no arguments. It
turns out that this is quite a common case, so it is worth optimising
for this, to reduce code size, before events become too commonly used.

Finally, it introduces a way of emitting an event in an initcall,
instead of calling a function. This is likely to be used at least as
often as the functions, as we convert more of these initcalls.

As part of this, the initcall code is brought back into a C file. Somehow
the compiler has changed or something else, so that this does not confer
any benefits now.

For boards with EVENT enabled, this unfortunately results in small
growth, e.g. for firefly:

   aarch64: (for 1/1 boards) all +114.0 data +16.0 rodata +22.0 text +76.0
       arm: (for 1/1 boards) all +82.0 rodata +18.0 text +64.0

For boards without EVENT enabled the growth is smaller, e.g. nokia_rx51:

       arm: (for 1/1 boards) all +32.0 data +8.0 rodata -8.0 text +32.0

I cannot find a good way to avoid the latter, other than macro magic
with an embedded comma (to completely remove an event entry), which
seems nasty.