[L] Change in flashrom[main]: rpmc: add rpmc commands feature

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Matti Finder, Peter Marheine.

Anastasia Klimchuk has posted comments on this change by Matti Finder. ( https://review.coreboot.org/c/flashrom/+/84934?usp=email )

Change subject: rpmc: add rpmc commands feature
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Patch Set 6:

(4 comments)

Patchset:

PS4: 
Thank you so much for testing!
> I used the dummy programmer with dummy:emulate=MX25L6436 which can then be handled as a "SFDP-capable chip"

This is great, I didn't realise that dummyflasher can handle SFDP chips, but yes indeed! I will write a test for this (not right now, but later in a separate commit)

File sfdp.c:

https://review.coreboot.org/c/flashrom/+/84934/comment/9be49bc7_41322878?usp... :
PS4, Line 457: if (sfdp_fill_flash(flash->chip, tbuf, len) == 0) {
             : 					ret = 1;
             : 				}
> Maybe this should return error straight away

I said that, but I forgot about freeing the memory :\ and now remembered.
Added two more comments (sorry), but that should be the last, everything else is done in this patch.

File sfdp.c:

https://review.coreboot.org/c/flashrom/+/84934/comment/7797f3ef_4c65e1aa?usp... :
PS6, Line 457: return 0;
We still need to free the buffers, so I think this should be

```
ret = 0;
goto cleanup_hdrs;
```

https://review.coreboot.org/c/flashrom/+/84934/comment/31c6385c_629ede2c?usp... :
PS6, Line 482: return 1;
I think let's keep the previous line (`return ret`), since `goto cleanup_hdrs` is called a few times in the existing code.