PCI: iproc: Add support for the next-gen PAXB controller

Add support for the next generation of the iProc PAXB host controller, used
in Stingray.

Signed-off-by: Oza Oza <oza.oza@broadcom.com>
Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>