MFC r268735:
Improve support for Intel Lynx Point USB 3.0 controllers by using the
USB 2.0 port mask in addition to the USB 3.0 port mask. The hardware
does not always accept when writing -1U to the port switching
registers.
MFC 261904,261905,262143,262184,264921,265211,267169,267292,267294:
Various PCI fixes:
- Allow PCI devices to be configured on all valid bus numbers from 0 to 255.
- Tweak the handling of PCI capabilities in emulated devices to remove
  the non-standard zero capability list terminator.
- Add a check to validate that memory BARs of passthru devices are 4KB
  aligned.
- Respect and track the enable bit in the PCI configuration address word.
- Handle quad-word access to 32-bit register pairs.