PCI: Remove unused PCI_SUBTRACTIVE_DECODE

PCI: Remove unused PCI_SUBTRACTIVE_DECODE

2fe2abf896c1 ("PCI: augment bus resource table with a list") added
PCI_SUBTRACTIVE_DECODE which is put into the struct pci_bus_resource flags
field but is never read. There seems to never have been users for it.

Remove both PCI_SUBTRACTIVE_DECODE and the flags field from the struct
pci_bus_resource.

Link: https://lore.kernel.org/r/20241017141111.44612-1-ilpo.jarvinen@linux.intel.com
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>