uefi: Implement PciRootBridgeIo bus device enumeration logic

[seijikun]

I finally gave up on trying to achieve the PCI bus device enumeration without allocation - that's not gonna happen.
I therefore accepted my fate and transformed my version with allocations into an upstreamable state.

This implementation uses the RootBridge's configuration() method to query ACPI information about the bridge. This contains ranges of valid bus addresses (setup & configured by the UEFI firmware), which are then used as starting points for the recursive bus/device/function scan.
The result of this recursive scan is written into a BTreeSet - which now has the ordering you'd expect and are used to from tools like lspci.

Best consumed commit-by-commit :P

Checklist

• Sensible git history (for example, squash "typo" or "fix" commits). See the Rewriting History guide for help.
• Update the changelog (if necessary)

[phip1611]

Thanks for working on this! And yes, I can imagine that using this nicely without alloc is a pain.

[phip1611]

there is plenty of functionality in that module not needing alloc

[seijikun]

But the rest only consists of private helper functions that aren't that useful outside. Do you want to expose them?