net/nfp: add NSP support for commands

net/nfp: add NSP support for commands

NSPU interface declares a buffer controlled by the NFP NSP service
processor. It is possible to send commands to the NSP using the NSPU
and this buffer for data related to the command. A command can imply
buffer read, buffer write, both or none.

Initial command for resetting the firmware is added as well which
does not require the buffer at all.

Commands will allow firmware upload, symbol resolution and ethernet
link configuration. Future commands will allow specific offloads like
flow offloads and eBPF offload.

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