[M] Change in flashrom[master]: sb600spi.c: Move promontory code into a mmap_read=yes mode

[Arthur Heymans (Code Review)]

Attention is currently required from: Jonathan Zhang, Thomas Heijligen, Edward O'Callaghan, Arthur Heymans.

Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/71565 )

Change subject: sb600spi.c: Move promontory code into a mmap_read=yes mode
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Patch Set 3:

(1 comment)

Commit Message:

https://review.coreboot.org/c/flashrom/+/71565/comment/62fa5ed7_bc250dea 
PS2, Line 10: This is not
            : hardware specific
> > I believe it is hardware specific to controllers after a certain generation. i.e., supported on SPI100 controllers (Zen etc) however not supported on pre-SPI100 controllers was my understanding.
>
> I think the parts controlling the speed and mode might not apply, but it is memory mapped for sure.

It looks like the speed params are handled correctly. Memory mapping should work on all AMD platforms.