[SPARC64]: Restrict PCI bus scanning on SUN4V.

On the PBM's first bus number, only allow device 0, function 0, to be
poked at with PCI config space accesses.

For some reason, this single device responds to all device numbers.

Also, reduce the verbiage of the debugging log printk's for PCI cfg
space accesses in the SUN4V PCI controller driver, so that it doesn't
overwhelm the slow SUN4V hypervisor console.

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