PCI bus bridges have standardized Device Tree bindings:

PCI Bus Binding to: IEEE Std 1275-1994
http://www.openfirmware.org/ofwg/bindings/pci/pci2_1.pdf

And for the interrupt mapping part:

Open Firmware Recommended Practice: Interrupt Mapping
http://www.openfirmware.org/1275/practice/imap/imap0_9d.pdf