x86/PCI: Add NumaChip remote PCI support

Add NumaChip-specific PCI access mechanism via MMCONFIG cycles, but
preventing access to AMD Northbridges which shouldn't respond.

Signed-off-by: Daniel J Blueman <daniel@numascale-asia.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>