[flashrom-gerrit] Change in flashrom[master]: spi_master: Use new API to register shutdown function

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Nico Huber, Thomas Heijligen, Angel Pons.
Anastasia Klimchuk has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/56103 )

Change subject: spi_master: Use new API to register shutdown function
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Patch Set 5:

(1 comment)

Patchset:

PS5: 
I rebased this, please let me know if there are any other comments that I should do (I am happy to work more on this if needed). I would keep going and do the same with par masters and opaque masters (actually I started already and wrote some tests CB:56470 and CB:56413). Technically pars and opaques are not blocked, but please tell me if there is something I am missing here. Thank you!