[efi] Allow discovery of PCI bus:dev.fn address ranges

[efi] Allow discovery of PCI bus:dev.fn address ranges

Generalise the logic for identifying the matching PCI root bridge I/O
protocol to allow for identifying the closest matching PCI bus:dev.fn
address range, and use this to provide PCI address range discovery
(while continuing to inhibit automatic PCI bus probing).

This allows the "pciscan" command to work as expected under UEFI.

Signed-off-by: Michael Brown <mcb30@ipxe.org>