Change in coreboot[master]: util/cbmem: Add FlameGraph-compatible timestamps output

[Jakub Czapiga (Code Review)]

Attention is currently required from: Tim Wawrzynczak, Paul Menzel, Alex Levin, Julius Werner, Jan Dabros.
Jakub Czapiga has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/62474 )

Change subject: util/cbmem: Add FlameGraph-compatible timestamps output
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Patch Set 4:

(2 comments)

Commit Message:

https://review.coreboot.org/c/coreboot/+/62474/comment/b8dd86ac_ad6faf67 
PS4, Line 15:      -t/-T/-S options
> Can you give an example flamegraph, or list how to create them?

I will provide more info in the commit message with the new version of this patch (splitting timestamp enums/string and cbmem changes)

File src/commonlib/include/commonlib/timestamp_serialized.h:

PS4:
> nit: I think this change could be split out by itself, also, if we're going to go with this mechanis […]

I think it is a good idea. First, it will help to avoid typos in strings. Second, it will provide direct enum->string mapping.
I will prepare an appropriate patch.