MFC 261904,261905,262143,262184,264921,265211,267169,267292,267294:

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.

git-svn-id: svn://svn.freebsd.org/base/stable/10@268887 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f