ARM: dts: NSP: Add PCI support

Add PCI support to the Northstar Plus SoC.  This uses the existing
pcie-iproc driver.  So, all that is needed is device tree entries in the
DTS.

Signed-off-by: Jon Mason <jonmason@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>