When two controllers are attached to a physical port (e.g. in the
case of EHCI and its companion controllers, problems can occur if
the BIOS still has control of one controller when we try to use the
other one. So perform a first pass to scan the PCI bus and take
ownership of and reset all the controllers we find, and perform a
second pass to initialise the controllers and probe for attached
devices.
As we don't support hot plugging, split the second pass into two,
with the first probing the EHCI controllers and handing over any
low and full speed devices to the companion controllers, and the
second probing the remaining controller types.
martinwhitaker