PCI: Add Broadcom Northstar2 PAXC quirk for device class and MPSS

The Broadcom Northstar2 SoC has a number of quirks for the PAXC
(internal/fake) PCI bus.  Specifically, the PCI config space is shared
between the root port and the first PF (ie., PF0), and a number of fields
are tied to zero (thus preventing them from being set).  These cannot be
"fixed" in device firmware, so we must fix them with a quirk.

Signed-off-by: Jon Mason <jon.mason@broadcom.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>