nfp: flower: implement the PORT_REIFY message

The PORT_REIFY message indicates whether reprs have been created or
when they are about to be destroyed. This is necessary so firmware
can know which state the driver is in, e.g. the firmware will not send
any control messages related to ports when the reprs are destroyed.

This prevents nuisance warning messages printed whenever the firmware
sends updates for non-existent reprs.

Signed-off-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>