net/nfp: support new firmware medatada API

net/nfp: support new firmware medatada API

We need to support how firmware metadata was handled until now and also
the new API, since NFP NFD 3.0 firmware versions. The new metadata API
adds flexibility for working with different metadata types and, mainly,
to allow adding metadata from different firmware components independently.

Although this patch just supports one type handled by the PMD, future uses
regarding firmware apps will extend this support.

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