boards: Remove per-board definition of board_init

[chrysn]

This removes the occurrences that can easily be removed automatically.

Command used:

sed -i -z 's@\n/[\n* ]*.brief[ a-zA-Z,().-]*[\n*/ ]*\nvoid board_init(void);\n@@' boards/**/*.h

Closes: #16007

Summary of #16007: Not all boards do it, so it's clearly not necessary, and the caller of board_init does an extern on it anyway; moreover, it clutters documentation, which should be "every board defines this to do X", not "we do X" for every board. (Notes about the concrete implementation should go to the implementation anyway).

This is not complete yet in that it only does the "easy" ones that are caught by a single-line regexp. A follow-up in here will go through the rest manually, but first I'd like to see how badly things fail.

Testing procedure

Builds still complete.

[fjmolinas]

Shouldn't this be included in board.h instead?

[chrysn]

I don't know -- at some point we get to choose.

A nice aspect of separating "that where the functions any board needs to provide" from "that where board-specific macros like LED0_ON are defined" is that it reduces rebuilding, and separates otherwise unrelated concerns.

[fjmolinas]

This is not complete yet in that it only does the "easy" ones that are caught by a single-line regexp. A follow-up in here will go through the rest manually, but first I'd like to see how badly things fail.

Seems not that bad.

[fjmolinas]

@chrysn do you think you could give this one a rebase and make it not a draft, I think we can get it in!

[chrysn]

I'll retry when my RIOT-unrelated workload is back to a level where I can; thanks for the nudge.

[benpicco]

48088cb has the removal of board_init() from board.h for the current master

[chrysn]

Thank you @benpicco for taking this over with a better PR, closing this in favor of #17707,