nfp: allow non-equal distribution of IRQs

Thus far the code assumed all vNICs will request similar number of IRQs.
This will be no longer true with control vNICs (where 1 IRQ will suffice).

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