PCI: hotplug: Use FIELD_GET/PREP()

Instead of handcrafted shifts to handle register fields, use
FIELD_GET/FIELD_PREP().

Link: https://lore.kernel.org/r/20231018113254.17616-4-ilpo.jarvinen@linux.intel.com


Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>