[M] Change in coreboot[main]: device/pciexp_device.c: Fix setting Max Payload Size

[Patrick Rudolph (Code Review)]

Attention is currently required from: Angel Pons, Arthur Heymans, Felix Held, Krystian Hebel, Michał Żygowski, Nico Huber.

Patrick Rudolph has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/77338?usp=email )

Change subject: device/pciexp_device.c: Fix setting Max Payload Size
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Patch Set 10:

(1 comment)

File src/device/pciexp_device.c:

https://review.coreboot.org/c/coreboot/+/77338/comment/d7cdb98c_33399de0 :
PS10, Line 709: pciexp_configure_max_payload
instead of adding all of the new code, wouldn't it be simpler to do something like this here:

```
/* Walk up the chain and adjust MaxPayload to the minimum supported in the chain */
while (dev->bus && dev->bus->dev && !pciexp_device_is_root_port(dev)) {
  ...
  /* Adjust Max_Payload_Size */
  pciexp_set_max_payload_size(dev->bus->dev, root_cap, dev, cap);
  dev = dev->bus->dev;
};
```

That way all of the devices are updated with the minimum supported MaxPayload and every time a new downstream device is added it traverses the chain up again to potentially set a newer and lower limit.
It increases the runtime exponentially, but as it's a corner case anyway it should have no influence on 99.9% of regular systems.