net/nfp: add NSP support for HW link configuration

net/nfp: add NSP support for HW link configuration

Adding a new NSPU command for being able to read and write the ethernet
port table from/to the NFP. This will allow the PMD to put the Link up
or down when a port is started or stopped. Until now, this was performed
by the firmware independently of PMD functionality.

The ethernet port table has also some other useful information that will
be used in further commits.

Usually NSPU is used at device probe time and that is sequential code
execution. However, reading and writing the NFP eth table can be done at
different times and from different cores, and it implies it could happen
a concurrent access. A spinlock is added to the global nspu object for
protecting the NFP and avoiding the concurrent access.

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