PCI: Separate CardBus setup & build it only with CONFIG_CARDBUS

PCI: Separate CardBus setup & build it only with CONFIG_CARDBUS

PCI bridge window setup code includes special code to handle CardBus
bridges. CardBus has long since fallen out of favor and modern systems have
no use for it.

Move CardBus setup code to its own file and use existing CONFIG_CARDBUS to
decide whether it should be built or not.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patch.msgid.link/20251219174036.16738-18-ilpo.jarvinen@linux.intel.com