nfp: centralize runtime reconfiguration logic

All functions which need to reallocate ring resources at runtime
look very similar.  Centralize that logic into a separate function.
Encapsulate configuration parameters in a structure.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>