For callers of pci_common_init_dev(), we previously always required a PCI
I/O port resource. If the caller's ->setup() function had added an I/O
resource, we used that; otherwise, we added a default 64K I/O port space
for it.
There are PCI host bridges that do not support I/O port space, and we
should not add fictitious spaces for them.
If a caller sets struct hw_pci.io_optional, assume it is responsible for
adding any I/O port resource it desires, and do not add any default I/O
port space.