net/nfp: add NSP user space interface

net/nfp: add NSP user space interface

Working with the PF requires access to the NFP for basic configuration.
NSP is the NFP Service Processor helping with hardware and firmware
configuration. NSPU is the NSP user space interface for working with the
NSP.

Configuration through NSPU allows to create PCI BAR windows for accessing
different NFP hardware units, including the BAR window for the NSPU
interface access itself. NFP expansion bar registers are used for creating
those PCI BAR windows. NSPU uses a specific expansion bar which is
reprogrammed for accessing/doing different things.

Other expansion bars will be configured later for configuring the PF vNIC
bars, a subset of PF PCI BARs.

Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>