net/nfp: support CPP

net/nfp: support CPP

CPP refers to the internal NFP Command Push Pull bus. This patch allows
to create CPP commands from user space allowing to access any single
part of the chip.

This CPP interface is the base for having other functionalities like
mutexes when accessing specific chip components, chip resources management,
firmware upload or using the NSP, an embedded arm processor which can
perform tasks on demand.

NSP was the previous only way for doing things in the chip by the PMD,
where a NSPU interface was used for commands like firmware upload or
port link configuration. CPP interface supersedes NSPU, but it is still
possible to use NSP through CPP.

CPP interface adds a great flexibility for doing things like extended
stats or firmware debugging.

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