Change in flashrom[master]: programmer: Introduce default shutdown function

[Joursoir (Code Review)]

Attention is currently required from: Nico Huber, Edward O'Callaghan, Angel Pons, Anastasia Klimchuk.
Joursoir has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/54890 )

Change subject: programmer: Introduce default shutdown function
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Patch Set 6:

(2 comments)

File flashrom.c:

https://review.coreboot.org/c/flashrom/+/54890/comment/df2d8e37_b59bda75 
PS5, Line 78: int default_shutdown(void *data)
> `static int default_shutdown(void *data)`

The reason why default_shutdown isn't static is because we're going to use it in the API. This helps us explicitly specify which of the shutdowns the programmer is using, e.g:

static const struct spi_master spi_master_programmer = {
  ...
  .shutdown = default_shutdown,
};

https://review.coreboot.org/c/flashrom/+/54890/comment/111fc397_944d3cb1 
PS5, Line 104: function;
> Yes, when I mentioned "shutdown function should be required" above, in my mind it was exactly this:  […]

Do I right understand that you mean checking in register_*_master() and not in register_shutdown()?

int register_spi_master(const struct spi_master *mst, void *data)
{
  ...
  if (!mst->write_aai || ... || !mst->shutdown) {
    return ERROR_FLASHROM_BUG;
  }
  ...
}