- pci_find_extcap() is repurposed to be used for fetching PCI-express
extended capabilities (PCIZ_* constants in <dev/pci/pcireg.h>).
- pci_find_htcap() can be used to locate a specific HyperTransport
capability (PCIM_HTCAP_* constants in <dev/pci/pcireg.h>).
- Cache the starting location of the PCI-express capability for PCI-express
devices in PCI device ivars.