Change in flashrom[master]: pickit2_spi.c: Refactor singleton states into reentrant pattern

[Nico Huber (Code Review)]

Attention is currently required from: Edward O'Callaghan, Angel Pons, Anastasia Klimchuk.
Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/52774 )

Change subject: pickit2_spi.c: Refactor singleton states into reentrant pattern
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Patch Set 1:

(3 comments)

File pickit2_spi.c:

https://review.coreboot.org/c/flashrom/+/52774/comment/39a5cbe4_1e92716f 
PS1, Line 57: };
Do we need this struct? I guess it would make it easier to extend in the
future, but this seems hard to predict. We could also pass the libusb handle
directly as `data`.

https://review.coreboot.org/c/flashrom/+/52774/comment/e1d4b973_7f01382a 
PS1, Line 343: static struct spi_master spi_master_pickit2 = {
This will bug me with every single patch. I think the API is just broken
and maybe we should fix it before making more use of it. The per-instance
`data` pointer should simply be passed to register_spi_master(), IMHO.
This might actually be easier to address right now as there are not that
many programmer drivers that use the `data` pointer yet.

https://review.coreboot.org/c/flashrom/+/52774/comment/0b21cbcc_982ab4fb 
PS1, Line 472: 	pickit2_data = calloc(1, sizeof(*pickit2_data));
No NULL check? (Could be avoided by not using a struct.)