Tons of enchancements to MD PCI code:
- The G-REX 4000 and G-REX 1200 are now really supported and working (still only 1st slot but the rest are a matter of time).
- Add bridge identification to p5pb, simplifies the driver and make it more user-friendly.
- Retire P5PB_GENFB and P5PB_OLD_FIRMWARE options, these are now handled automatically, depending on used hardware and firmware.
- Add PCI bus reconfiguration support to p5pb (PCI_NETBSD_CONFIGURE), allows using G-REX without boot to AmigaOS.
- Bring p5pb registers desription up to date with my knowledge.
- Add a lot of debugging code to p5pb (enabled by P5PB_DEBUG kernel option).
- Fix PCI_NETBSD_CONFIGURE in mppb (now it really works).
- Fix quirk handling in zbus.
- Update GENERIC.in and regen the kernel configs.
- Misc cleanup.

(rkujawa)