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
......................................................................

Patch Set 3:

(2 comments)

Patchset:

PS1:
> > I have a message to reviewers, thank you! […]

Yes this raiden_debug_spi is implemented differently and this causing me troubles second time, and I have to spend time on it... I want to write init/shutdown test for this one next, because test is super cheap to run, however both times it would detect a trouble! and save me time.
Sorry not that much relevant for this patch, just complaining :)

Patchset:

PS3: 
I tested on two different devices and updated commit message. Just wanted to do a spot check, given that the change is the same for all programmers.