Change in coreboot[master]: timestamp: Add new helper functions

[Julius Werner (Code Review)]

Attention is currently required from: Bora Guvendik, Furquan Shaikh, Selma Bensaid, Tim Wawrzynczak, Subrata Banik, Angel Pons, Aaron Durbin.
Julius Werner has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/51445 )

Change subject: timestamp: Add new helper functions
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Patch Set 8:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/51445/comment/74566f2e_80d0a6b4 
PS3, Line 7: Add helper fucntions
> > Julius, please see the following 2 patches, I implemented your suggestion (hope understood correct […]

Yeah, I don't really know what you did there to be honest... you just flipped the negative sign into positive on all the negative timestamps (with your `tse->entry_stamp = 0 - tse->entry_stamp;`), why did you do that? Of course they'll be in reverse order and completely incorrect compared to the positive ones then. I think if you had just added your rebase_delta to all timestamps (positive and negative) you would have gotten resonable results (and shouldn't need to sort again).

But, anyway, I think that code could have been way simpler. Please see my comments.