PCI: Introduce pci_resource_n()

Introduce pci_resource_n() and replace open-coded implementations of it
in pci.h.

Link: https://lore.kernel.org/r/20230330162434.35055-3-andriy.shevchenko@linux.intel.com


Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>