[SPARC64]: Force dummy host controller onto bus zero.

This helps deal with the invisible bridge that sits between
the host controller and the top-most visisble PCI devices
on hypervisor systems.

For example, on T1000 the bus-range property says 2 --> 4
and so there is a PCI express bridge at bus 2, devfn 0, etc.

So if we don't force the dummy host controller to bus zero,
we'll try to create two devices with the same domain/bus/devfn
triplet.

Also, add some more log diagnostics to make debugging stuff like this
easyer.

Signed-off-by: David S. Miller <davem@davemloft.net>