Add a PCI bridge for the Freescale PCIe Root Complex

[jhibbits]

Summary

The Freescale PCIe Root Complex shows up as a Processor class device, PowerPC
subclass, so the generic PCI code ignores it for a bridge. This adds support
for it.

As part of this, update the Freescale PCI hostbridge driver, to allow probing
beyond the root complex, instead of only allowing "proper" PCI-PCI bridges. An
alternative, which is #if 0'd out currently, is a hack to force the secondary
bus to 'primary plus 1' if a stable PCIe link is detected. This makes the
assumption that PCIe can never have more than one bus, but it's not as elegant
as the solution I proposed. However, the solution proposed may see false
positives, and has not been tested beyond the MPC8544 in the RouterBoard RB800.

[imp]

looks OK, but I'm not an expert...

sys/powerpc/mpc85xx/pci_mpc85xx.c

269

Do or Do Not. There' is no #if 0.
:)

sys/powerpc/mpc85xx/pci_mpc85xx_pcib.c

2–4

Odd copyright for a new file.

[jhibbits]

sys/powerpc/mpc85xx/pci_mpc85xx.c

269

I included this as the 'very unsexy alternative' mentioned in the summary. Soliciting opinions in case someone objects to my chosen solution.

sys/powerpc/mpc85xx/pci_mpc85xx_pcib.c

2–4

D'oh. That's what I get for copying the copyright+include list header.

[jhibbits]

Address copyright comment. Also, add a new function, pcib_bridge_init() to
clear the bridge config and use it in the new driver.

[nwhitehorn]

Nice work! I agree about the #if 0 section, though -- please remove it when you commit.

[jhibbits]

Committed r282783.