Change in coreboot[master]: Documentation: Add proposal to allow enabling serial console with a flag

[Arthur Heymans (Code Review)]

Attention is currently required from: Paul Menzel, Stefan Reinauer, Julius Werner.
Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/54385 )

Change subject: Documentation: Add proposal to allow enabling serial console with a flag
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Patch Set 3:

(1 comment)

File Documentation/technotes/2021-05-selectable-serial-console.md:

https://review.coreboot.org/c/coreboot/+/54385/comment/7b09a841_04874626 
PS1, Line 112: and change the default to whatever is found there.
> SGTM in general, but you removed the part about forgoing the bootblock now? That part is still important -- remember that non-x86 platforms can't access flash until a lot of other initialization in the bootblock has happened. (Also -- this is just something to keep in mind for the implementation -- you'll need some safeguards to avoid recursion when the CBFS code tries to print things.)

Even on x86 this could be important on some setups. For instance with Intel bootguard/CBnT the RO part of the flash is not considered trusted so depending on ro only cbfs access should be avoided.