lspci: zero address in IO isn't always unassigned

lspci: zero address in IO isn't always unassigned

Zero is a valid address in I/O space, so display it and it's associated
size when IO is enabled in the PCI command register.

From arch/powerpc/kernel/pci-common.c:

/* Here, we are a bit different than memory as typically IO space
 * starting at low addresses -is- valid. What we do instead [is] that
 * we consider as unassigned anything that doesn't have IO enabled
 * in the PCI command register, and that's it.
 */

Signed-off-by: Aaron Sierra <asierra@xes-inc.com>