MIPS: PCI: Support mapping of INTB/C/D for pci-xtalk-bridge

Implented mapping of PCI INTB/C/D, which is needed for PCI multifunction
devices, PCI-PCI bridges and IOC3.

Signed-off-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
Signed-off-by: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-kernel@vger.kernel.org