PCI: iproc: Add BCMA type

The iProc PCIe driver is currently using type IPROC_PCIE_PAXB for the
following SoCs: NS, NSP, Cygnus, NS2, and Pegasus.  In fact, the BCMA-based
NS uses a legacy PAXB controller that is slightly different from the PAXB
controller used in the rest of SoCs, e.g., some registers are missing and
it does not require software configuration of outbound/inbound address
mapping.

Add a new type, IPROC_PCIE_PAXB_BCMA, to allow us to properly support the
BCMA-based NS along with other iProc-based SoCs going forward.

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>