Separate out pci_add_dynid() from store_new_id() and export it so that
in-kernel code can add PCI IDs dynamically. As the function will be
available regardless of HOTPLUG, put it and pull pci_free_dynids()
outside of CONFIG_HOTPLUG.
This will be used by pci-stub to initialize initial IDs via module
param.
While at it, remove bogus get_driver() failure check.